I think the signals are there and you are deciding to ignore them. You already said he acts different. You saw with your own eyes that he has an interest in someone on myspace and now you say you have sex and he drops you off like you are a random chick or a booty call. You are 18 so you are young and have your whole life ahead of you. This dude is not treating you like you deserve to be treated. Move on before you get hurt worse. Have some dignity and self respect. He is no longer interested in you the way he used to. He definitely likes someone else but is not man enough to end it. As long as you put out he is going to take it, but his heart seems to be with someone else........Take Care