I feel a very clear distinction between the two, though I'm having a hard time putting it into words exactly what the qualitative difference is. The physical aspect of it is the most obvious and easiest to explain; there is just no way that any desire for physical contact could ever come from even the deepest friendship, while even the mildest crush makes me want to get all hand-holdy. Other aspects are tricker and more nebulous, but there are a lot of romancey feelings I get that I don't get to any degree from friends. Maybe if I was really close with a friend I think they're an amazing and interesting person to the same degree as I would think that of a girlfriend, but even at the same intensity it would feel different. And the drive to be around someone all the time and share my life with them just doesn't exist with friends. I enjoy their presence, but I don't obsess over them no matter how strong that friendship may be.

Bah. Explaining emotions is tricky, there aren't any proper words for any of it. I hope that made some amount of sense, anyway.