One of the boundary issues that I would talk about seriously with him is from now on, no more lying. On your side though, you have to be willing to listen and discuss things with him as well. The betrayal seems like it's a much bigger deal in your world than the fact that he was sexual with someone else. Rubuilding trust isn't something that happens overnight.
Everything will be ok in the end. If it's not ok it's not the end.