My (22F) partner (22F) cheated on me with our mutual friend (29M) 2 months ago. They are both working in an office - only two of them. On the day of cheating, they were laying on the couch and talking about emotional stuff - then our friend asked her is he can kiss her and they kissed. After that, my gf asked him to kiss her again. She found out that she's in love with him (he's also in love with her) and at first my gf asked me to be in a poly relationship - I said no, because I don't really see myself in such relationship, at least for now. We started couples therapy a week ago and we both go to IC.

We decided to stay together and work on our relationship. At first I asked her not to go to the office, but 3 weeks ago I told her it's ok and she's been there three times (she goes once a week). But honestly, I fear Tuesdays when she goes to the office. I feel relief when Wednesday comes and when it's Monday I feel awful, because it'll be Tuesday soon. I feel that I lash out on my gf and feel so so angry inside and I feel that it's not fair to her, but I just cannot regulate myself when I know she's going there. I am so scared that something is still going on between them or that even if something physical doesn't happen, I'm scared that going to this office makes her fall in love with him even more - they take breaks at work and talk about deep emotional stuff. Our friend told her that he doesn't feel as if he can cry in front of his wife, so he wants to talk to my gf and cry when she goes there. It makes me so uncomfortable - I told that to my gf already. Before the cheating, it was perfectly fine for me, but I feel so much pain when I'm alone at home and think about her being there. I'm also very anxious about them texting on Messenger - I never saw these messages because my gf said it's private and that this guy also said some private stuff on there, so she doesn't want to show it to me. And I know that's her right - I'm trying really hard to trust her that there's nothing going on, but sometimes I'm scared that I never saw those messages. But still, I see how that would be invading privacy.

We were on a trip on Sunday and it was really great, I missed such time with her. And yesterday I got triggered that she stopped saying that she's heartbroken about not being able to be with this guy (also with me) in a relationship, so I asked her why she stopped. She said that she stopped saying these things, because she doesn't want to hurt me, but she missed him a lot on this trip, which made me feel miserable. I know that I asked about that, so I should blame myself, but it hurts so much that she's in love with him and I feel as if it's not going to change. I'm so in love with her and I always was for the last four years. It hard to deal with her having such feelings for someone else too, because I don't feel that she wants to get rid of them - but maybe it's unfair of me to expect that. She also said, that yesterday she texted him "Can't wait for tomorrow to talk to you" and it also hurt me. Which is not fair, because I know they're friends, but it just sucks that bot EA and PA happened. I don't know how to handle all of this in a healthy way. I just feel sad, scared and hurt. I'm also always so happy when my gf dresses nicely when she goes out, but since the affair it even hurts that she dresses in clothes that are (in my opinion) the most beautiful - it's ok that she does, but I feel anxious what's behind all of this.

Some days are so great and I stop thinking about her feelings - but then it hits me. I don't know how to deal with the fact that there's contact between them and I feel that I sometimes treat my gf unfairly, because I know that he is her friend also.

TL;DR: My gf cheated with out friend, who she works with alone in an office. She's been there 3 times since cheating and I'm having a hard time dealing with it emotionally. I'm anxious and angry on Monday, the day before she goes to the office and tell her that I'm scared about what they're doing there. I'm tired of feeling so much and have no idea how to deal with that.

I would appreciate if you tell me how it's possible to deal with these emotions and express them in a healthy way. Now I make anxious comments and tell my gf every time "to not do something stupid", remind her my boundaries, tell her that I feel anxious about her going there and that I'm scared there's something happening between them. I also asked her to tell me when she'll be going back home (tell me before leaving the house at which hour she'll be back and if it changes - inform me) and also I asked her to text me a few times a day. Before cheating I was so happy that she has a place she can go to and work in comfort, and also have a chat with her friend. And now I feel like a piece of shit and don't know how to deal with that.