Any ideas as to what could be wrong?

I was talking to a guy before he left for a missionary trip for 2 weeks. We talked practically all day in the days leading up to his departure for Africa. We couldn't talk while he was overseas, so it was really hard, but I knew that once he returned, we'd pick right back where we left off. Turns out, that didn't happen. He returned roughly 2 weeks after he left, and it was as if we'd experience a complete 180. We talked only a few minutes of triviality, and saw each other once. I refuse to initiate a conversation because I feel that if he truly cared, he'd make an effort to talk to me. I'm being stubborn I will admit, but I've already proved how I feel about him. Should I wait for him to make a move, or just completely abandon ship? Thanks guys.