Tbh I still dont think its "crushes" thats the problem. I think its not acting on it before you get too emotionally invested thats the problem. If you've gotten your energy focused on one woman or man like Spartan said, and have not made any attempts to act on it then yeah that can be like drinking a slow acting poison.
Yes, this.
I mean, you shouldn't be afraid to fall in love if someone is really that great... but you need to make sure you're not actually in love with something in your own head instead of a real person. When you don't make your intentions clear, you end up second guessing everything and reading things into it that aren't there.
I'm not sure if it's what Spartan meant, but I don't think that most people would repelled by someone's exclusive interest... I don't meet many women who I feel are worth the effort, but when I do I put 100% into it and if they don't appreciate it then it's their loss.
On the other hand, being aloof can be frustrating or suspicious and often backfires, especially in the long run. Being rejected is one of the risks of putting yourself out there, so I don't think that the pain of rejection is something that can ever be avoided. It's just part of life... instead of trying to avoid it, embrace it as something you need to go through in order to get to a better place.
I don't think people outgrow crushes... why would they?