You two just don't have the same ideas of what it means to make a commitment to someone you love, and that fact becomes more and more apparent the more you communicate. You could even be very attracted to each other and really want to make it work, but with this aspect between you, that definitely takes plenty of compromise and communication -- which isn't your strong point. You try to talk things out, but you usually just end up arguing.
The longer your relationship goes on, more and more of these little misunderstandings happen, until you just feel completely misunderstood by each other! After all, one of the most important things in an intimate relationship is to feel close on a mental, intellectual level. You want to be matched up with someone in that way, so that you can talk easily and get where the other person is coming from. In this relationship, a feeling of commonality and ease like that is hard to find. You might even treat each other in an intellectually patronizing manner, especially if other aspects between you make you competitive or otherwise support a feeling of tension. Even if you really want to make a commitment to each other, it could be hard because it just doesn't mean the same things to each of you, and it's hard to figure out where the mismatch is coming from.