Why do guys treat me like crap?

I'm probably one of the nicest people you could ever meet. I'm open-minded, very understanding and sympathetic, I go out of my way to help people and I don't act fake or judge anybody. I have a great sense of humor, I naturally make people laugh and I'm very social and approachable. I see the beauty in everything and everyone. I care about what's skin-deep, I have never cheated nor will I ever. When I fall for a guy I fall hard, I treat him like a prince. I'm pretty attractive (not trying to sound cocky), but lots of guys just want to get in my pants. I'm not desperate, but I want to find a guy that sincerely cares about me and doesn't treat me like crap. So many guys who I thought were my guy friends would get so jealous and get mad at me over nothing and would start calling me a slut if I even gave my number to a guy... they talk sh*t about me or they just completely disrespect me to my face. My ex did the same this to me after a while. I just don't know what's wrong with me, they make me feel terrible for everything that I do. :( I just don't understand how they could talk to me that way and make me feel horrible every day, when I'm one of the most sensitive and kindest people they know. Why do some guys treat certain girls this way?
Why do guys treat me like crap?
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