My best friend (M24) and I (M23)  have been as close as brothers for years. A few months ago he met a girl and they got serious very quickly, and he says he loves her. She seems like a nice girl and theyre a great couple and I know he is happy, but ever since he started dating her he's becoming more and more distant. He spends a good amount of his free time with her and when he's with her he wont answer his phone. He still makes an effort to see me and his other friends but when we're hanging out he's messaging her constantly. I also feel like he tells me less and less about his day to day life now, like we still talk a lot but it doesn't really have any substance, I just get short responses or really generic answers. He'll also spend a few days with her at her place and then blow off other plans afterwards because he's tired. 

 I know I should be happy for him and I'm probably being a juvenile asshole for feeling this way but I miss my friend. He's still the most important person in my life, and I'm not the most important person in his anymore. 

So, AITA? 