I agree with what Kari said. If you guys were such good friends (and it sounds like you were) you should be able to talk to him about this.
I've had the same thing happen to me. I had a good friend and when he got into a relationship he would stop talking to me, usually because the girlfriend didn't want him talking to me. Jealous?? Anyway, he got married 5 years ago and I haven't heard from him since.
Try not to get hung up on him. He's obviously doing his own thing and you should too. If you two are meant to be together it will happen. Maybe further down the road when he matures a bit more.

And welcome back!!