Why are some guys so sweet and others such jerks?

All a girl wants is a nice, fun-loving guy who doesn't care how big your are or how anerxic you are. I found a guy who is super sweet and I told him I liked him and I totally got shut down, even though he was nice about it and said he still wanted to be friends, It still hurt like hell. A year before I totally got led on by a guy who embarressed me infront of everyone. I just want to know why the perfect guy seems so amazing and he turns you down, yet the skinny blonde can get him. What the hell is wrong with this world??? ♫ (oh p.s I'm on my friends account so this isn't sammy)