Don't have time for a long response just now, but two quick responses:
My roommate is about 90% aware of the situation. All four of us involved are fully informed of exactly how everyone else feels, and the things that haven't been divulged yet are untold simply because someone is still mulling them over and/or isn't ready to discuss them yet further; no steps will ever be taken without everyone being 100% aware of everything that's going on, or 100% on the same page.
And no cheating will be happening on my watch. I told him that if he ever cheated on her, he'd be dead. Yes, even with me. I would be neither able nor willing to defend him if he did that to her. I love her too much. And I love him too much to let him do something that stupid again. After what happened last time... yeah, that's definitely #1 on my avoid list.
Thanks for the tips