How do you fall in love?

I'm 20 years old and I don't know what falling in love is like, but I really want to. I've had a few crushes but it's never been a big deal when they were with someone else or moved away. I've also had one relationship but I only agreed because I thought making myself be that intimate with someone would be the key. Once I realized it wasn't working, I explained and we agreed to break up (still great friends though). I can't even seem to get into dating. Is something wrong with me? Are my hormones not working or something? Or is it just something mental? Help...