I posted this over in r/bisexual as well, but thought folks here might have some words of advice or different words of advice, or someting to share.

My(M45) wife(41F) and I have been together for almost 2 decades. We don't have any kids, by choice. We dated for several years and lived together before we got married. We are strictly monogamous. Our sex life is AMAZING (actually only getting better with time). We did not disclose sexual past/specifics before we started our relationship, and even to this day we haven't disclosed any specific numbers, although have shared some details, but more on that later. (we're both adults and realize that we have had other partners - but we both wanted a fresh start/clean slate, so we decided that the past didn't matter and I feel like that was truly the best course for us. We were both tested and clean and have only been with each other since getting together).

When we were first dating she did mention to me that she had a relationship in college with another woman but since she was with me, I assumed that it was simply experimentation. (I went to drama school so I have seen my fair share of experimentation, and even participated in some myself, but only went so far as kissing, turns out it wasn't really for me, and that's ok.)

When we were first together she mentioned something about threesomes. Knowing that I would be too immature to handle it, I quite vigorously said something to the effect of "I would never want that at all". (but deep down I really really did)

Fast-forward to present day (about 2 months ago) and we were watching a movie and she mentioned something about how hot a certain actress was and how much she'd want to kiss and go down on her, or someone like her. I was a bit surprised and we started talking.

We had a very frank and very open conversation and she told me "I'm bi-sexual, you know that". Which I was surprised about, telling her that I knew she had tried dating a woman in college but I thought it was a failed experiment. She let me know that the most significant relationship she had before me was with a woman, and it was for ~3 years. She referenced that past conversation where she said that I essentially made her hide her true self, because she knew how against it I was.

I was shocked and saddened that I made her feel that way. It was never my intent. I apologized and I told her how honoured I am that she is with me and has stayed with me for all of our life's ups and downs. (we've been through a LOT together) I also explained why I reacted the way I did, because I knew I would be too immature to handle it. I've also articulated how proud I am of her for finally telling me in no uncertain terms how she truly is. Of course also I love her, all of her, and never want her to feel like she has to hide anything from me and that I support her to be fully herself, no matter what.

Since then we've had several more talks and I've asked some questions (with her permission) and she's been very open with me (as I would be with her if she asked). She's had both sexes as partners and has had threesomes in the past (which I will admit I’m jealous of the experience). I've had my fair share of sexual partners, but have never had a threesome, I've shared this with her, also have shared that it's a huge fantasy to have a FFM threesome with her. (I think an even bigger fantasy for me would be to have a MFM threesome with her...but that's a whole other subreddit/kink, I think.)

We talked about the idea of a threesome and she has made it clear that although she is bi-sexual she chooses me and our monogamous relationship above all, and will not risk anything getting in the way of that. Although she did say that if we were to have a threesome I wouldn't be allowed to penetrate the other woman, because she'd be too jealous; and she says that wouldn't be fair to me or to a potential partner...so it's best to just leave it alone and let it live in our fantasy world.

I have told her that if she feels that she would like to have a girlfriend to satisfy feelings/emotions/physical needs that I can't provide (obviously I'm not a women) - I fully support her, and I mean it! So long as I'm in the loop from the beginning and know about it. I would only feel "cheated on" if I didn't know before hand. She says she doesn't want this as she is more than satisfied by me.

Since our conversations - she's even "come out" to some of our friends so that's cool - and I'm so proud of her for living her truth and being herself and I expressed this to her. (I don't think she will ever come out to her family though.)

The upshot of all of this is that we can look at hot women together, which is fun! (turns out we both really like breasts)

I guess the only thing that I would ask for "advice" about is how to stop feeling so turned on about thinking about her being pleased by/pleasing another woman? Am I sexualizing her sexual orientation? Or just her? (since I also think it would be so hot to see her be pleased by another man...) I love this woman more than anyone else I have ever known in my life and I love giving her pleasure.

Since we've talked she knows that this is "new" for me and we openly talk about everything so this isn't a secret to her, but I still can't help feeling like I'm a bad person. As mentioned - our sex life is AMAZING and I don't feel the need to be with anyone else, but if the option was open, and especially to do so with her would be exciting.

I hope it's just normal excitement about finding out something new about the love of my life that I've been with for 20 years - similar to how I found out she was an amazing writer a few years back.

I suppose I'm also wondering if there are any books I should read or other posts/resources to look up to help me support her and make sure she feels safe and loved. (Which I think I'm doing a decent job of already.)

OR just if anyone else has had a similar experience and can share their story with me?

Feel free to ask me any questions/details that I may have forgotten.

Thanks for reading all this and I appreciate any feedback.