95% chance that your "guy friend" liked you and felt like you used HIM for 3 years as he got nowhere with you, before he finally snapped and did whatever he did to hurt you. That would explain why he no longer cares about how you feel.
Girls: if you have single "guy friends", chances are very high that they are your friend only because they want something more (sex for sure, but often a relationship), and that's why they hang around and listen to your problems and give you advice and so on. Often, they hope and assume that becoming your good, close friend will increase their chances of making you their girlfriend. But let's be honest: you and I both know it almost never works like that, because you "don't want to ruin what we have." But the only reason you HAVE what you have is because he has always hoped for more. And so at some point, he's going to realize that it's never gonna happen, and then he is going to feel used and bitter for wasting all of that time and attention on you.
This does NOT apply to a guy who has a girlfriend or who has an active dating life; that guy can be your friend without such motivations. But if he's single? No way.