how do you know?

how do you know you really love someone?

i was talking to a friend of mine the other day, and he was saying that he really loved this girl and he was crushed that she didn't love her back. which is normal. but he was telling me it had always been her, even for the long periods of time when they weren't together (after they'd broken up). which came as a bit of a surprise, as that's not the way it had seemed to me. now, i know my friend has a habit of not telling anyone anything and of being really secretive, but still... to make that kind of statement, i would kind of expect to have seen something of that amazing love he says he holds for her. it is just wishful thinking on his part? for example, i remember a few years ago when another friend found out this guy she'd known forever was getting married. she was crushed because she believed he was it, the man of her life, despite having never even dated him. again, i'd never heard any of this before, hadn't even known the guy existed. she was very depressed for a couple of months and even wondered whether to tell him how she felt. as i recall, she tried, but obviously not hard enough, as he happily went on to marry the girl in question while my friend hit rock bottom. but a few months later, she saw the newlyweds, and boy was she happy she hadn't married him after all. seeing them together made her realise what her life would have been like and she was incredibly happy to have escaped marrying him after all.

so, back to the question: how do you know that you're really in love with someone and not just wishing? here, both of my friends obviously had an idea of who they wanted their loved one to be and so i wonder, are our expectations realistic? are we just scared to think that we haven't yet met our person so that we choose someone we know as a safe bet?