This guy won’t respond to me, AT ALL, what do I do?

If your positive hes seeing those messages then you need to stop letting him take advantage of you. Next time you see him face to face ask him what's the deal between us is he gonna take the relationship to the next level or is he gonna keep doing this. Ask him if he has feelings for you If he says yes don't kiss him till he ask you out if he says no just walk away he's just using you for pleasure

This may sound crazy, but how about you ask him the next time you see him, "Dude, WTH??" If you like his answer, game on. If not, move on.

u need to talk to him next time u guys meet,if he tries to kiss you again stop him and first ask whats the deal between u guys? u have to talk to him and get things sorted out soon otherwise ur feelings may get complicated.

Do other people know about it? Since he is your best friend's brother, does that mean he's older? Or maybe younger? Maybe he's ignoring you because, even though he likes you, and maybe can't resist doing things with you while you're around, maybe he's afraid of it becoming too real or serious, because he's worried how other people will react if they found out. If you are serious about him, and you guys really get along, I would just express those feelings of how much you like him, and ask him if he's worried about other people finding out. If he says that he is worried, just tell him you like him, and want to be with him or whatever, and if he's worth it, he'll stop ignoring you.

The logical answer would seem to be that he only enjoys you for kissing. No need to complicate things by caring about how people feel and stuff. Stop offering him the kisses, and he will surely lose interest in you entirely. Problem solved!