Hey blankcanvas - welcome to the forum no one wants to be a part of, but we are all here  

I am sorry you are here, but glad you found us. I think it would be helpful to consider several things:
1. her sexuality is not the point, the only point that really matters is she is choosing someone else and not you. My ex wife said the same initial "I want to want us, but I just want her" she said. Just because someone is bi, doesnt mean its not cheating. Cheating is cheating. period.
2. She is putting all of this on you. "If you want to stay together, I will make it work" she said. That is a massive grand canyon sized red flag that not only is she not done exploring, she wants you to function as a parental figure and make the decision for her. Thats not a healthy relationship....
3. Actions matter, words do not. Just because she says she wants to be with you, what are her actions showing you? If it is you that consistetly has to say the right things, do the right things etc, where is her accountability? 

I can not decide for you. No one care. Take the time you need and focus on YOU. Clearly, that is what your wife is doing, focusing on herself and not you at all. Words DO NOT matter. Only actions.

Be well my friend. Its a long journey, but life gets really good on the other side. I am in a healthly relationship now and looking back at my marriage, it was not only toxic, but it was manipulative in every way. 

Hi blackcanvas

Sorry to find you here.

You do need to step back a bit, it feels like you're spinning. It's hard, but many people have been through it before and so will you!

This forum is helpful, if your goal is to separate, most people on here will steer you in that direction. If you want more balanced advice try these groups on Facebook:
https://facebook.com/groups/mixedorientationrelationships/
https://facebook.com/groups/morandmorecommunity/

I strongly recommend couple's counseling to move you guys through the crisis. Polyamory can be enjoyable and if you want to explore it, you need to equip yourself with some new knowledge and also un-learn a few things. Read "Ethical Slut" if you're into reading. Don't believe the scaremongering that opening the relationship is the point of no return. You can easily open your relationship and then close it again (my bi husband and I did, so do many other people).

Good luck! You got this!

Hi blankcanvas - I'm really sorry for everything you're going through.  It's confusing and heartwrenching. 

I'm with Blackie - curious about the part in your post where she said that if you wanted to make things work, she would break it off with the person she's with.  Sounds like she wants to make YOU responsible for whether you're together or not, when it's actually HER looking elsewhere that has your relationship unravelling.   As far as divorce goes - I think there are more than a few people on this forum who are glad to be divorced instead of married to someone who'd rather be with a whole different gender, whose attention is directed outside the marriage while we're at home wondering what we could do to improve the relationship.   In my case, the GXH pulled out all the stops to blame distance and conflict on me.  Divorce is a fresh start.  

Monkey branching into a new relationship, means that she will need a firm hold of the old one before deciding to let go and discard you. If the new one still has issues where she cannot fully commit to it, she will play both camps for as long as it suits her. A has been said, actions count much more than words. Do not stay in a relationship with a lesbian when you are contemplating children in the future. She has already shown you that  she will leave you for a woman if the chances are there. If this happens down the line when you are a father, the implications are going to be horrendous for you and your children. You have been given the opportunity to dodge a bullet that I was not given. That, or you take it for her. You could end up as the sperm donor and the free childcare that she needs to live her authentic life. You seem to be a great guy, with your heart in the right place. This heart should sit next to the heart of a straight woman who is committed to you and the relationship as well. You don’t need to accept this amount of disrespect in your life. She wants to be be gay, or bisexual or whatever she wants to feel she is to suit her own needs. That is her problem not yours. Also, if someone tells you to look somewhere else for a more ‘balanced’ view, it is because they are trying to suggest that this view is more balanced than any other. What I will say finally is, that if you accept her and her behaviour now, this normalises it. In the future, she may use this to assuage herself of any conscience challenges when it comes to the next woman she develops feelings for.

in my experience it's the ones that make you feel good that you have to watch out for the most.  

There was this woman who told me she was having relationship problems, she was sleeping in her van and I said she could stay in my studio for three nights.  I found myself pushed around by her without even realising it was happening and then I noticed that I was waking in the night feeling concerned and wanting to talk it out with her and yet as soon as I spoke with her it went away and I felt like everything was completely fine and it was only the following night that I woke up still feeling worried and realised my concerns hadn't been addressed or answered at all.

I asked her to leave the next morning.  Guess who came to help her move back out of my studio (she had filled it with stuff) - her boyfriend.  Turned out to be a nice man, I felt sorry for him but tbh was mainly glad she was moving on from me.

My favourite line in Ordinary guy's post - "You don’t need to accept this amount of disrespect in your life."

I don't know what happened with the girl you met but that sounds much more promising.  Or maybe someone new will come along.