I was in the same situation, you did well by not telling him about what you saw, because he'll think that you're insecure about yourself, and that you don't trust him.
Since he's treating you the best, and bragging about you to his friends (that's a big step btw), he is definitely in love with you, and he wants you to trust him.
The fact that he gave you his cel shows that he has nothing to hide and he wants you to trust him.
For the "recent" part, his ex might have called him recently maybe to apologize about what she did, but he obviously moved on, remember that YOU'RE the one who made him move on, so you should be secure about yourself and not doubting about what he does with his ex because that is already over long time ago.
Guys keep in touch with old gfs because they think that it's cool, they're not that sensitive as girls are, so they just forget what happened and move on as friends and not more.