I think its great that you didn't gush all over him when you found him in the house, and that he had to pursue/initiate. Also how you didn't put XBF completely out of the picture, and it was good that you had showings to do. All good boundaries and GAL stuff.
I'm sure when he says he didn't cheat he means he didn't have sex, and I'm sure that he's very proud of himself for that. He probably thought he deserved a medal or something for his "self-restraint." I've been there. He has no idea how hurtful it was for you to have to listen to him describe his dates--he really thinks that you should be proud of how he "matured."
It sounds like you were able to show your disapproval without totally ripping his head off. That's probably about the right approach for now.
He's still got a lot of work to do, talking about "at most" a "platonic" relationship with someone else. BS. What he means by that is, he wants to lead other women on, just for the ego boost of being desired. Then he gets to pat himself on the back for "resisting temptation." At some point down the road, you'll have to explain to him that a platonic friend of the opposite sex is someone you are never alone with.
