What does it mean when a boyfriend exclaims he doesn't want...?

Sounds like he got scared and instead of telling you why he felt this way he attacked you, you both got defensive, and it got blown out of control. To be honest I would be a little bit upset about his answer and ask him just what he was doing with me in the first place, and what he wanted out of the relationship, etc. Sometimes people get a little nervous when talking about huge commitments like family, marriage, etc and they don't know how to communicate and they react the way he did, but I don't yet have a reason to think he really wanted to truly hurt you, though his reaction was a bit overblown/immature from what I can gather. You can always start the conversation again on a better foot by talking about how you felt when he told you these things and try to get him to open up a little more by asking him why he doesn't see a future with you. Once you get a few more answers you'll know then if you want different things and should move on or stay together.