What's going on in his head? Why does he do this?

Ask him out and ask him what he's been up to. You should ask him what he wants from you in any type of relationship. Don't let him confuse you or hold you back from anything because that's not fair for him to do to you. If things are cooling down, and you want them to be like that, let them be. Though, if you want to continue talking to him, suggest a 'date' and casually talk him into it.