Well personally I think that everything can't keep you constantly happy and can't keep you constantly sad; everything is just balanced out to keep your feelings, overall, neutral. Love is the same. Love can be an incredible feeling, but it's such a fragile feeling that barely anything can break or damage it.
As a teenager, you tend to over-react with some things and ignore the good something causes you and focus on the bad. Which is why you make such a huge deal about when you get dumped or something, you just think that things can't possibly get any worse and that Love is pointless and a waste of time because you always end up crying about it. That's not true, because you're ignoring all the good times you had when you were in love.
But I also think that you only have one true love in your life, and that's usually the person you marry or decide to spend the rest of your life with (if you don't wanna get married or whatever). Some people get married without thinking, and end up getting a divorce, but your true love is the one you stay with forever, through the good times and the bad.
Love is unlike any other feeling, but let's not forget: the bigger they are, the harder they fall...