My brother may well be a ?

well, I'm just real worried about my brother. he wants to be a woman. I ain't saying I love him any less, the idea just don't sit too right with me. He's still my brother, so despite my feelings I aught to support him. but I'm not really sure though if I can consider him "trans gender" he still acts like a guy to some extent, he says he fells like he'd be more happier if he was a girl, but I think he still considers himself as a "he" to some extent. He's a bit emotional, but he ain't real keen on wearing a dress. says he wants to be a girl but tough or something. I really didn't mind, up until I herd him seriously talk about actually getting a -change. I know I should let him do what he thinks is best for his happiness, but I don't know, I'm just real worried is all.I guess I just need advice or something