She says she missed out on being single in her 20s because she's been with me the whole time and I didn't because I am older and got to play around so I owe her. The deal is she asked for 90 days of open marriage to get it out of her system and then she wants to start over. She thinks it will take away the resentment she's been harboring for some time.
I think this is quite a normal feeling, and I can certainly relate - if you didn't get to experience much variety in partners over your life, I think the curiosity will always be there. But I don't like how transactional things seem with you guys. You don't "owe her" for the fact that you got a different set of life experiences to her, any more than she "owes you" the chance to get off on her personal sexual experiences. If she feels resentful towards you over this, then that's a big red flag waving in the wind. She has to accept it was her choice to date you in her 20's, and not something you 'took away' from her. I would be really disappointed and hurt if I felt like my lover thought the formative years of our relationship were an inconvenience to them that stopped them from getting laid more.
I also think the 90 days thing is potentially a bit unworkable. What if she doesn't find anyone in that time? What if she finds someone she clicks with? Setting a hard limit like that could end up being too restrictive, or lead to her making an agreement with you that she later wants to break, which could break your trust in her to follow her word. If I were you guys, I would be asking her what the 90 days is for, and perhaps working more towards there being no limit as long as everyone is happy and feeling respected.
She will not go to therapy with me. She says I just don't understand.
Forgive me, but this is insane troll logic. She might be right in that you don't understand, but then that's exactly why therapy might be useful. You don't avoid therapy because you currently don't understand something. You go to therapy IN ORDER THAT YOU MIGHT BE ABLE to understand in the future.
But as of right now after having sex with another guy for the first time during our open marriage she says she didn't like it and she discovered it's not what she's looking for or missing in her life. But it may come back again in the future.
This exactly. So she hooked up with someone that, for whatever reason, didn't do it for her. That's not going to change her craving for perhaps exploring and hoping to find someone that DOES do it for her. Hence why putting any kind of time limit on this endeavour is doing you both a disservice.
The reason I had a differing understanding of how it would be is because she knows that hearing her describe fictional sexual encounters with other men turns me on and we use it quite often during foreplay.
Well, I do hope you have learned a lesson about assuming things without explicitly discussing them. I too enjoy making up (and hearing made up) stories of me or my partner fucking others during sex. It's hot. However, that doesn't mean either of us necessarily want to put those fantasies into reality. If she presents a scenario I'm actually interested in, when we're lying there all sweaty afterwards, I tend to ask her directly: 'So, that thing you were saying when you did that other thing that felt great? Do you actually fancy trying that sometime, or is it just a nice thought?'
Sometimes she will use examples of the times she cheated on me too.
This seems like relevant information to just drop in all casual like. So, she has cheated on you in the past. Is this part of why you are uncomfortable with her dating others without you being there? Do you, on some level, worry she might betray you again in some way? Not be able to stick to agreements in some way? Start to seek out a romantic attachment? I think if there are any lingering trust issues between you guys, you need to fix those before either of you hooks up with anyone again. In all honesty, I'm seeing a lot of problems between you both: you don't communicate well, you're not direct with your emotions, you both seem to bottle up resentment and fail to take responsibility for your choices. Seriously, I think you guys need some external help in sorting through this stuff. If not a therapist, then a really good non-judgemental friend to you both.