Because you are in a super-casual non-committed relationship with a guy who’s simply not that interested in you (and he’s a jerk just because even if the other parts are true, people shouldn’t say they’ll meet you and then not show up, it’s not polite, no matter who’s doing it).
It’s sounds like what you’ve got with this guy is a “friends with benefits” kind of thing (even if you haven’t yet or won’t ever have sex). He’s not your boyfriend, so he’s probably getting loving and cuddling elsewhere too.
You have a few choices about what to do about it:
1. Next time he comes over, have a frank discussion about your “relationship” with him. If you want a boyfriend/girlfriend relationship with him, you need to tell him that, and that you have strong feelings about him and that you want to know how he feels about you (don’t accept any wishy washy sorts of answers like, “I like you, you know that. ” or “It’s fun hanging out with you.” without any sort of real idea about where you and he stand. Be prepared for the potentiality of his dumping you on the spot or his attempting to place blame on you for “blowing everything out of proportion” or trying to smooth things over with sweet talk and not fixing the problem. If you really want a “real” relationship with this fellow, you need to let him know how bad it makes you feel when he says he’ll come over and then doesn’t show up. The way he reacts when you tell him that will tell you a lot about his character. He’s likely to take one of two approaches. Either he’ll say something like, “I’m so sorry that I’ve been acting like a jerk, how can I make it up to you?” or “What’s your problem? What the big deal? I’m not your boyfriend! Why are you being so possessive?”
2. You can tell him that you enjoy his company, but you feel like you’re in a kind of a limbo situation with him. Not really together as a couple, but more than just friends and then ask him what he wants to do about it. But also let him know that you feel really crappy (your feelings are hurt) and annoyed (because you feel like you’re waiting on him and can’t make other plans) when he says he’s coming over and then doesn’t. You might suggest that you two remain friends, but cool it with the cuddling and other physical stuff, because you are, in fact, just friends at this point. Let his reactions and words be your guide as to what to do next.
3. Drop this guy like a hot rock. If he calls to ask if he can come over, very casually let him know that you don’t think it’s a good idea for the two of you to hang out any more because you don’t really see this relationship going anywhere and you think that it’s just a little bit too casual for your taste. He may say “That’s cool.” and you’ll never hear from him again, or he might say, “What’s your problem? We’re just friends, you shouldn’t read more into things!” or he might say, “But I like hanging out with you, can’t we just hang out?” To which you should reply, “It was fun, but no.”