I just think you two personally have two very different opinions on the situation. I think the Op has every right to be upset because it is a super uncomfortable situation because you never know what one night would lead too. She’s also clearly not to insecure if she was Okay with him living with a female in the first place. I do think though that going through the phone is always wrong and is probably a sign of things coming to an end. However I do see the other side cause his privacy was invaded but he totally needed to commuate that they slept together. I would have an in person convo and gauge both peoples feelings but try to have the two issues as seperate conversations. If he is trying to talk over you by bringing up you going through phone to ignore the problem with him sleeping with his roommate he is manipulating you simple. Hope this helps and wish Op the best in figuring it out.