How do you handle a friend who acts moody and quiet?

I used to date this guy (just briefly). Every time I see him out, he acts really quiet and doesn't talk to me. I know its not a problem with me, it's his personality. He's kind of moody and doesn't say a whole lot, unless the cirstances are perfect or if he needs something. He does talk to some people more than others though, and I'm not sure why. My problem is that I feel really bad because he gives me no attention, but he can be a really cool guy, or atleast he used to be. I feel bad after I've been around him, like I've been ignored. I don't think he's consciously trying to do that. I have brought it to his attention (delicately) and I can see where he's tried to make an effort, but it falls way short of what I would like as a friend. I certainly don't want to make any demands of him and I'm trying to accept him for who he is, but I keep getting really frustrated and feeling ignored. Can you help me?