Not the easiest question to answer! But I'll try.
1)Most people, when they think they are in love, get a nice buzz from it that is sort of addictive.
That is sexual attraction. Nice! But
on it's own it is a relatively short-term thing and when it fades you start looking elsewhere.
2)When you share a lot of interests and enjoy each others' company without needing to leap into bed with each other,
that's friendship.
3)When a relationship with another person just means getting what you want out of it,
that is neither friendship nor sexual attraction.
4) When your relationship with another person means you consider that person's welfare to be of prime importance,
regardless of your own interests, than that relationship is valuable.
5) Put
1,
2 &
4 together, chuck
3 out the window, and
you just might have a case of real love! 
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