Sibling problem ?

My little (20 year old) brother is in the military and was dating this girl for just a few months when they eloped before a deployment. I initially raised my concerns about her and her intentions but he got so defensive that I've pretty much learned to bite my tongue about her if I plan to have any sort of relationship with my brother. Well she proved me right and cheated on him throughout his deployment, but he still took her back when he got home. Then she came to meet our family and was a total witch the whole time. Now they're pregnant. When I got the call I wasn't very good about hiding my lack of excitement, but I immediately texted him and apologized, by which he responded to by ignoring me for a week. I just don't know what to do. I feel like I'm the only one who puts effort into maintaining a relationship, but it's hard when his life revolves around this manipulative girl. And now she's got him trapped for life. I really do try to grit my teeth and smile, like i'lI try to ask questions about her and her pregnancy, but it's so one-sided. I almost have no interest in even talking to him because all he's interested in talking about is him and his life, and has no interest in mine. I just feel defeated ?