Not to be a philosophical jerk myself, but loss is the nature of life and love. If you're not willing to deal with loss, you might as well never get up in the morning. If you're not willing to seek out positives from defeat and rejection, that'll just grind you down in the long run, because if you can't affirm the value of your own feelings - even if they were in vain - then you're going to forefeit whole years of your life while building up more and more unrealistic expectations. That's where healthy fatalism, rather than pure cynicism, is helpful - in the end, you lose everything anyway, and value in life isn't found in trying to desperately hang on to things and people, but in making the best of what you have/had while you can.
Unrequited love is a bitch and it hurts, but you can still take away a lot from it. You just need to stop angry about it and disengage yourself from it first, then you might just end up looking back on it as something very good. Where it becomes a problem isn't loss, but denial. It's where you can't let go of feelings, however hopeless they are, nor can reformulate your relationship with that person into something that's manageable for both parties.
Personally, I'm far more upset that it's now been slightly over a year since my last serious (but hopeless) crush than I am over my failtastic love life that's been composed of nothing but unrequited feelings and lost causes. Cause even those weren't so bad, really, and sure made things interesting while they lasted. I'd rather feel engaged in emotional futility than emotionless cynicism. I find the latter a lot more poisonous, energy-draining and difficult to live with. That's my purely personal take on it, anyway.
Then there is, of course, the issue of trauma. Rejection in love? You bet that can make for some pretty nasty trauma, but that's not something that you can cure with pills, or somehow reverse by going back in time changing things. It's not even something that a sudden success will reverse or erase. It's something that you have to learn to deal with. Yes, by that logic, it might seem like a better idea to avoid it rather than live with it, but you get to a point when it becomes no better than a phobia. Sure you might end up wanting to avoid cars if you ever get into a car accident, but are you really going to be better off never driving in the future? Would you really rather be stuck to things in walking distance from you than get in a vehicle? Does it make all the places you've been to thanks to cars before you had the accident worthless?
I'm not saying at all that it's not a big deal - it is. But you can choose to shut down over it, or learn to live with it. And it's much easier to live with anything when you realize that hey, that had lots of positive aspects to it too, and the wreck that you ended up in doesn't really cancel them out.
