What is love?
Now there's a question. The big mama of all questions other than 'why?'. Love is supposedly letting them go, but that's only half of it. Love is letting them go and missing them like hell forever more. That's the part they never tell you. It isn't just blood, it isn't just mind, it transcends all of this. You may hate it, you may 'love it' but Love is a strange and twisted master/mistress. You may see you are being irrational, you may fool yourself into thinking you are okay and over it, after all; It's just an impulse. But it returns. You cannot control it.
Most relationships are not with people you necessarily love, you just think they are. Most love, around 90% is unrequited. That is how some relationships last so long. Each person realises the person they love doesn't love them so they settle for someone who seems to really like them (there is a difference). It makes them appreciate someone who cares for them all the more. Plus just think how bad it would be to go out with someone who really did love you or who you really love? Walking on egg shells/tense emotional problems over everything/etc.
The purest love is always the unrequited. There is nothing there to taint or spoil it or the image of the person. Of course they aren't with you, why would they be? More to the point if they love you back there is the possibility for them to act or do something that is different to being 'just friends' that may warp your perception of them. You may end up hating themů But if you love them then that should never happen!...