I know you don't want to hear this, but there is no way you will ever know everything. He can have a dozen different FB accounts and email addresses that you don't know about. There is no open book unless HE allows it, and you will never be guaranteed that you know everything.
People can change. I personally know someone that did change, and I am grateful for that every day. And from the moment the promise to change was made, I had ZERO doubts that he meant it and did it.
You guys need some serious hard core heavy duty counseling. This is not something you can do on your own. It's just not.
Trust is also an important part of marriage, and it works both ways. If you feel you need to control all his social contact, does he have your information for all your passwords to social networking and email? While I don't agree with the cutesy baby talk, I can see why he'd find that and the attention from her appealing. It seems you never actually forgave him for the cheating, and are looking for a reason to refuel those emotions.
He cheated, once. And instead of doing everything in his power to make you feel that it was a one off mistake, it seems like he's done even MORE things to erode your trust. Not cool. You're an adult and so he is. No one should be in a situation where they have to keep constant surveillance on their partner to make sure they aren't cheating. Playing Secret Spy is emotionally draining, and life is short. You deserve to be with someone who will not make you feel this way.
I wish you both the best with the counseling, but frankly none of this sounds like a recipe for happy.
