I felt like that never was explained clear enough after Murray said he thought he was light in the loafers. I always thought he was kidding and Christian was just shy. If he was gay, why did he go out with Cher and seem affectionate with her?
You actually question this? I figured it out when they went to the party. He didn't look at any other girl because he was checking out other guys. And started dancing with another guy when she was dancing with her back to him. It was pretty obvious.
"Oh my God! You put a living room where the crack den used to be!"
Murray told Cher that and she confirms it by groaning in embarrassment and basically laughing at herself for being so dumb. So she confirms it for you that he's gay.
I believe Christian liked her for her personality and fashion and lifestyle, so he became good friends with her. They were basically fashion buddies. He was her GBF (Gay Best Friend).