My opinion is that he is gay, and given on what his brother might've gone through coming out, maybe he's scared to come out. I'm not saying it's excusable, but regardless whether he is gay or not, his behavior is not acceptable in any capacity.

I know it's something you want to figure out, but what good will it do? The signs are clear that he isn't to be trusted and you shouldn't stick around to find out. Let him come out on his own time (if he is in fact gay) and by then you'll have moved on.