Hi....i get attahced to women very easliy...and then get hurt..help?

Im the clic example of a guy who falls for women who show a little interest and then somewhere i get heartbroken cause the popular guy comes on the scene and takes them away from me. I know i am a good guy who has a big heart and a likable person. But i suffer from a big insecurity, that "better guy"comes along and takes the girl i like...don't know where this insecurity has come from but i wish i neva had it...its not only negative but inhibits my relationships..any advice???