Why does he do this?

So, I found out yesterday he spent weekend putting up christmas lights on the OW parents house with her dad. I could never even get him to put up an ornament on our tree! He never wanted anything to do with the holidays, took no pleasure in going to get a tree. Spent every Christmas drunk. I found this out yesterday (before I fixed the block error this morning). I am angry, they are going to have their first Christmas, apparently a nice one. Meanwhile he still is asking me to go over. Why does OW get what I always wanted and asked for? Why is he filling his apt with the things I talked about wanting? Why is he taking the hopes I had for the future and making them HIS?