Update: Wife (Megan) met with Jill and told Jill that I'd hid a text from Megan. (I'd sent a text to Jill about sex. Megan found the text. I hadn't known that Megan Han found it. Megan asked me if I'd sent a sext to Jill. I denied it. Megan confronted me and told me she'd found it. She was mad that I'd lied to her. She wasn't mad about the content. She was also mad because our rule had been than I'd show Megan the texts that I sent Jill or that I get from Jill. Jill knew that I had been showing Megan selected text. She knew that I hadn't been showing all of them to Megan. Jill didn't know that I was breaking Megan's rules. I didn't like Megan's rule about having to show all the texts. I was fearful that if I'd shown her this specific text that it would have caused Megan to be jealous and that she would want me to cut off my relationship with Jill. She tells me now [and I believe her] that she was fine with the contents of the text, just not the fact that I hid it and then denied hiding it.)
Megan met with Jill and told her all that. Jill now knows that Megan has a rule, and I broke it. Jill and Megan are friends and seems like they still are. They've been joking and laughing on the phone since this reveal. I don't know what Jill really thinks about me now since I can't speak to her alone. We can have three-person texts/emails. Megan now has access to my phone and computer and can search for anything. (Including this post.) Megan doesn't trust me, and I've given her reason not to. I chose to save my marriage and give her full access and a promise that I won't communicate with Jill without Megan knowing about it. And I plan on sticking to that promise if it means that this is what is required for Megan and I to remain married. My marriage is very important to me. Yes, I feel bad if Jill runs for the hills, but Megan is my life. I suspect that Jill is mad at me for making her a part of my mess and for getting cut off from something that she thought was fun, through no fault of her own.
The three of us exchanged a couple of flirty three-way texts and emails yesterday, but it's hard to know what Jill is really thinking since she has to speak to both of us at once and because she knows that I must report everything that she might tell me.
I'll be very surprised if Jill sticks around. (And Megan, if you're reading this, I hope you see that I am putting you first and I hope that me posting this isn't a violation of your trust. It's an outlet, and I recognize that the responses that this post may garner are those of an anonymous online forum--which can be wildly critical and harsh without any real-world repercussion; so I take their comments with a grain of salt. Your opinion is what matters to me ultimately. Again, I'm sorry for putting you through all this.)