Don't let her play mind games on you. She cheated and is cheating, plain and simple.
You did not enter a marriage knowing this about her and she did not consult you before she started having sex with someone else. That is cheating and grounds for divorce in most states.
There are only a few ways these things end;
1) You set hard boundaries, such as she may only play if you are involved. etc. But that is all after she makes amends for cheating, which she did and is doing against your will. Calling it prison is asinine.
2) Open Marriage. Still she must make amends for cheating.
3) Divorce.
I'm almost 7 years from a similar situation. I'm still in my marriage, but I'm not sure really for how long, if I had to go back in time, I would have filed papers the day after finding out. The process is too difficult, end result is not guaranteed by any means, all the work and hurt can be rendered useless.
From the tone of your post, I suggest you visit MarriedRedPill on Reddit. r/marriedredpill and r/askmrp
You need to focus on yourself as well during this. The mindset there will help you.