I know how hard this is for you. My exABF moved in with the "other woman" as soon as I caught him. Even thought I put him out, it was horrible to be without him. They spent Thanksgiving, Christmas and New Years together and I was totally miserable. A mutual friend kept telling me what they were doing. I finally realized that it was too hurtful to hear about him, so I cut off contact with our mutual friends and total NC with him. I couldn't believe that it actually helped.
One of the things that saved my sanity was reading all the classic stickys on the forum. I cut out several of them and put a copy in my purse and one beside my bed and I read them every day. They really helped me remember what a jerk he was. I also asked myself what I missed so much about him and if I could find that with another person. I realized that it wasn't him I was craving, but companionship and someone to talk to several times a day. My friends filled a big part of that, and it really did get easier as time went on.
One of the things he did was go to my neighbors house several times a week. My neighbor would always tell me what they were doing. I realized that he never liked the neighbor very much and was just going over there so I would hear about "how happy he was". If he was that happy I don't think he would have to make sure I heard about it. I think your ex is doing the same thing. If someone is in a relationship and it's working for them, they don't have to contact their ex to share the good news.
Stay strong and keep doing what your doing. Listen to some music and read the stickys. This forum helps so much. It's been 5 months for me and I feel alot better than I did. The NC helped more than anything else for me.