Husband cheated. We want to fix things but says I can "break even." Should I?

So, here is the story, my husband cheated on me. I know everyone's first thought is to just leave him....but we have been together for almost 8 years and married...not even a full 3 months yet. His now ex roommate dumped his girl friend and left the apartment, like 5 minutes after he left she came down stairs and supposedly pressured my husband into sex and basically grabbed him by the D and lead him to the bedroom. She went after him so she could sneak in his room and sleep there at night because she would have been other wise homeless...I saw a few of the texts she sent him before and after they had sex the first time and it all backs up what he told me...the next day they had sex again because she blackmailed him. I even saw the text "Come meet me at my car and F*** me or I'm telling them." "Let me in the apartment, I need to shower before work. Don't make me tell them." The 3rd day he refused to let her back in the apartment or go to her car and have sex again, so of course she told me and his roommate. I'm not at all justifying what he did...he hurt me so badly. All he had to do was say no the first time or tell her to leave and it wouldn't have happened....but in the end we are seeing a marriage counselor and we are trying to work it out.

I've repeatedly said it's hard for me to even try to get passed this when I feel like I'm the only one suffering for this. Sure he has the guilt to carry....but I feel like no matter what I do I lose here. If I leave, I lose. If I stay, I lose. I want to go, but I really want to stay too. And so...he says why don't I "break even" and go sleep with someone else...but I know how wrong that is. Could our relationship survive 2 affairs? It really would make me feel better, but I know how badly it would hurt him and it's just so wrong and spiteful...but at the same would make me feel better.....but if I was going to do that then why not just leave him? I'm so tired of always being the one to get burned and just once I would really like to burn them back....I'm so lost I don't know what to do.