He does sound rather nice.

Your statement about cheating is not watertight, though. Had it been the case that people cheated because they no longer wanted to be with their original partners, then, they would have simply moved on without cheating. But his reaction to that hypothetical indeed shows that he won't divulge sensitive information, embarrass the ex gf, or do other unseemly things. So the cheating hypothetical was a good way to assess his post-break-up potential.

Would it help break the ice if you present your disclosure this way:

"Oh, I have been meaning to tell you but an opportunity has never come up. Let me then just tell you right now - I have a BDD, and am getting better already, but still occasionally have my low moments. This is just for you to be aware of - there is no goal-oriented activity expected of you."