I was with my ex for five years. He got married a couple of months after I left.
Crummy as it feels, it really isn't about you. He hasn't changed, except that his addiction is still progressing. All the mental health issues he had are still there. This new relationship is just another way of self-medicating. It will eventually implode just like everything else in his life. Right now is the honeymoon period. You know what comes after that. The criticism, the verbal and emotional abuse, the emotional yo-yo you endured.
Also agree with Suki. Tell your friends that you don't want to hear it. That's pretty crappy and immature behavior on their part.