For me, I think it varies quite a bit. I'm not terribly well versed in my own emotions. But I do fall in love, and, well, lust. And I am pretty sure I know the difference. It can take me time to grow to know and trust someone. I actually can be aware of the possibility and try not to think about it to much because I'm not sure it would work. I kinda failed miserably in one case. Just comes all at once. I can remember the exact moments and the exact triggers. I have never been prepared to deal with and understand the emotions involved, might be getting better with that.