Recently, my husband and a close mutual friend of ours have become very close. This friend is a lesbian, a very masculine one...with a fiancé she is in love with, so of course I've never had any issues with the friendship. that is until recently. I read some texts between them this week, and was shocked to see that both him and her were talking to each other in a way that neither of them should have been...especially not him. Calling each other "boo", telling each other they loved each other. Him texting her at work, asking if her "sexy ass" was still slaving away. Both of them telling each other often how much they missed each other, and him responding with "I need some of you in my life". He also went as far as to let her know that she "is absolutely the most beautiful, amazing person" he's ever met. When I confronted them both about this, she apologized immediately, telling me she should've told me about him being direct, but she never thought he ever meant anything by it in a romantic manner, and she certainly didn't...as she doesn't condone cheating or sneaking around. He responded with telling me I was paranoid, worried about nothing, that she "is one of the dudes", just his best friend. 

I decided a few days later to do some investigating myself. I found the pinger app, which allows you to create a real phone number, and text and call VIA this app. I created an account, went into his phone while he slept, blocked her REAL number, and swapped it out for the pinger number. I was curious to see if he would text her like this any further. The very next day, he texts her, telling her I'm "crazy", and apologizes to her for my behavior, because she didn't deserve to be drug into it. He also lets her know that he put a password on his phone, and she can continue to call and text him "however she fucking wants". So I use the next few days to be "her": making small talk daily, asking about mine and his relationship. Nothing unusual. Until this morning. He texts wishing "her" a merry Christmas Eve, I ask if he works, he says yes, and asks why? Then asks if I'd maybe like to get dinner after he leaves work. I ask if the real me would be upset by this, and he says he didn't plan on telling me, that what I don't know won't hurt me. So I kick it up a notch. I pretend to "confess" I may have feelings for him, just to see what his reaction would be. He totally buys in! He asks if they're anything like "what I told you in the car ride home from work" (I still don't know what this was...), so I say yes, and that im ashamed because he's married and I'm her friend as well. He said he understands completely and he has feelings too, but they can't be ignored. So I ask if he would be willing to "try" something with me, if it wasn't crossing a line. He says "absolutely! I just don't want it to be something you regret". This is my breaking point. I call him and tell him he's busted, and that me and her devised a plan a few days prior, after I was upset about the original texts, to see if he would take it further, and he did. He tells me he "knew" he was being set up, and that's the only reason he said any of it.

What should I do?