I've thought about love about as much as the average person (if you take my sister out of the equation, 'cause she spent her whole undergraduate career on it. And I mean that seriously, not in a bad way.). I had a whole class on it first semester, what it is, and how it relates to our relationship with God, and what qualities we desire in a mate, and what drives us to pick who we pick. After all this thinking and wondering and comparing different situations, I think I've come up with something.
The only kind of love that exists is the kind you believe in. If you believe in love at first sight, then love at first sight exists. If you believe love doesn't last, your love won't last. Sure, there are exceptions, but the love you give and take is so colored by your perception of what love is, it will be conformed to your ideals. Love is like faith - love is a kind of faith. It is what you make it, what you believe in, what ideals you've created for yourself. Someone might try to tell you otherwise, but in the end, you know that what you believe in your heart is true.