Fiance doesn't want sex

We have been together for almost 7 years and up until recently we have a pretty good sex life. We have a 6 month old baby but for the last 2 months he doesn't seem to have any interest in me at all. He doesn't come to bed with me he sits up until I'm asleep or until he thinks I am. He is not affectionate towards me at all to hugs no kiss nothing. Any advice on how to talk to him about it or what I should do