Hey there, me and my gf are both new-ish to polyamorous/open relationships and trying to find our way through the ins and outs.

I want to describe a situation that has recently occurred and would like to get some pointers if possible.

A while back, me and my gf went to a friend's house party. Once there I noticed a good-looking guy and had this gut feeling that my gf is going to be interested in this person, who is the best friend of a shared friend of ours. She proceeded to soon grab his butt near the pool. He later picked her up and threw her with himself in the pool. Moves I consider boundary-lowering actions "hey we've already been body to body wearing basically nothing". We spent some more time at the party. Then, trying to be a trusting partner I spent a few minutes away from her. When I got back the guy had her "playfully" tied up in a rope and was dragging her into the cellar bar, she was finding it very amusing. Shocked but trying not to look like an idiot, I, in front of like 5 people watching, tried to pull her back up the stairs but they kept going until he ended up tying her to a hook in the ceiling in the cellar. This will come up again later. The party ended, we went home and I tried not to think about it too much anymore.

My gf is a dance teacher for bachata, and the guy from the party then started showing up at her dance lessons, which I also attend. Again, I didn't think too much of it.

Then a week ago, me and the gf decided to go hang out with our friends at a friend's place for some pre-drinking. My gf then sat down on a couch and gestured for me to sit next to her, which I appreciated and proceeded to do that. In walks guy from previous party. He sits down on the bed. My gf gets up and sits next to him on the bed. I immeditately noticed a shift in both her attention and in the general mood between the two which I didn't appreciate. Reason 1 our rule of no involvement within our friend circle (which at this point he was clearly in [also she already had 2 exceptions, the host female friend who she has sex with and another female friend she had sex with but was somehow off limits for me "because she had wanted to sleep with her for longer"), reason 2 no flirting with others in front of the other out of respect, and reason 3 me wanting to enjoy an evening with her and friends without having to worry or think about who in the room she wants to have sex with. So what I did was get up and sit in between the two. Guy stands up, sits on a chair. Gf gets up, gets a chair, says "she needs to stretch a bit" and sits on a chair next to the guy. Except for me and the gf, everyone at the party was single, so it was like 6 single men, one female single friend of ours. We played a party version of jenga clearly meant for singles or people who agreed to this. The game played out in that the guy had to drink a body shot from my gfs belly button. Later they had to swap tops (my gf doesn't war bras) and she was basically about to just rip her top off and I hopped in and basically held my shirt in front of her to change into his sweater. The game ended and we went into a private bar to play some billard, when I got in a few minutes later, I went to pee earlier, my gf and the guy already formed a team but I was invited to play with them. At one point I then asked my gf and told her I would prefer she didn't take this guy home to which he basically told me not to worry and she won't. A bit later I was tired and went home. Next day she comes over to me (she lives basically next door) and says we need to talk. She goes on to tell me they had kissed after I had gone home and that she realized this was probably against our rules and that, after the fact, she had explained that to the guy.

I told her that I felt disrespected by her and by the other guy for just thinking it would be ok to just hit on somebody's partner (apparently somebody had informed him of our open relationship and that made him think everything goes) without asking first. As a consequence, I felt I could not attend this weeks bachata lessons without making myself look like an idiot by confronting the guy there about it and not being in a generally bad mood while trying to dance with people. So now I feel disrespected by my gf and this guy, I feel ignored at a party I went to with my gf who only had eyes for the other guy. I am also made to feel guilty about not seeming to be ok with an open relationsip after all. I also explained to her that I had that gut feeling the moment I saw the guy at the previous party and explained the situation with the tying her up and that it seemed super out of character for her to do as what I would call a strong independent women and that I was basically made to publicly fight for my girlfriend in a sick tug of war kind of game that I lost. She at first didn't want to believe that that was what was happening until I described it in detail. I then explained that from my experience, this is something some men do as a kind of domincance move, discrediting someone's male partner by demonstrating his "inferiority". The more I think about this one situation the more I realize how fucked up that was to do for someone, and by extension, my gf to entertain and partake the whole thing. The next thing was that all my gf later apologized for was that she had not talked about this being ok or not beforehand, to which I replied that even if them doing whatever they wanted would be ok by our rules, if this is actually something she would want in her life The example I give here was that at this party with the billard game we were in a room where there was her female friend she sleeps with, her other friend who she has an almost sexual relationship with and has cuddly sleepovers on a regular basis, her other friend who she would like to sleep with but can't because rules. So I said in addition to that room already being filled with people you have slept with or want to sleep with would I want to go to a party for a relaxing evening with friends and then not knowing who of the people there you go home tonight instead of me this time and then would we want to add yet another person, this person being the guy from the party, on top of this? She then said no that's not what she wants either.
But she also said that my move of sitting in between them obviously trying to signal that I was not ok with their flirting was an asshole move on my side and that she saw this as something that made her double down on her behaviour.

Anyway, I could use some input on things in general here. We both know and acknowledged that we made our mistakes at some points here (we both also agreed that the alcohol consumed, which was more than we had both intended, was an obvious influence here). I also don't know how to handle the bachata lessons from now on, I am not super keen of running into this guy any longer.

In addition there have been a quite a few situations in which I was unsure what was going on. It's been a pattern I recognized that we harmonize extremely well when we're spending time together, but whenever we're at a social gathering I seem to be getting 5% of my gfs attention at most. There was her birthday party in march of this year at her flat. A girl I liked showed up there, my gf ended up making out with her in front of me. In confusion I also gave that girl a small kiss on the lips, no tongue or anything, I was recently made to apologize again for doing this. Later, at the same party, she was making out with another female friend of hers. She had not even kissed me that evening. In another bout of seeking comfort or attention or love or anything I later went up to her and wanted to kiss her, she turned away, I immediately said goodbye and went home (rejection disphoria in full effect). This is also something I brought up again when we discussed the recent incident with the guy, that she had made out with him there and that she had made out at her birthday party with the two women and, being frustrated, I said "all you need to know is comparing all this to the times you have made out with me at one of these parties, which is zero".

Then there is the thing that I'm not really someone who has an easy time at picking up women, and not many women seem exactly interested in me, which makes my situation harder for us in general. On top of that whenever I do sense that there might be something that could happen I am very mindful to not make my partner feel awkward, bad or bring them into a situation that is really uncomfortable. Example 1: gf was at a bachata festival in Greece. There was a chance that someone might be interested in me but we were only officially meant to be doing a fotoshoot for her, still, I did speak with gf about the possibility. It turned out that a possible date for this to happen was one day after my gf would return home and I decided to postpone the photoshoot so as to have time for my gf and it not being uncomfortable. Meanwhile on her second to last day I had asked my gf to have a phone call with her as I missed her, she said she didn't have time. Turned out on that last day of her festival where she didn't have time for a phone call she did have time to sleep with a guy though. Example 2 recently: I had by chance seen someone on tinder (which I rarely ever open) who was looking for a bachata dance partner. I discussed with gf and we agreed this could be good as I also want to practice dancing and if more happens that could be good as well. We both then realized that this could lead to uncomfortable sitautions given the Bachata scene is relatively small and we would be meeting running into each other and we both would like to avoid this, so I stopped persuing this, the woman then unmatched me. So again in trying to be mindful of my partner I rejected an opportunity only for her now making out and wanting to sleep with one of her students, the guy from the story above, which has indeed made it very uncomfortable for me to attend her courses.

Thanks in advance and I apologize for the probably pretty weird structure of what I wrote. I blame it 50 % on my adhd brain and 50 % being absolutely confused by the situation at hand.