Hopelessly in love: Why is that guys I like never liked me back?

I never understood it. The cute guys I like or guys I think are cute don’t like me back or always like my smaller female friends. I mean some tall guy flirted with a shorter girl and when I tried flirt, he just gives me a weird look and walk right pass me. I’m 5’11”3/4, large built and 249lbs (lost three a pounds).
One time, my petite friends (4’11” - 5’3”) and I were hanging out and guys flirted with them and ignored me. Guys would walk right pass me. Even guys over six feet don’t hit on me. Only short guys. I try so hard to get guys to notice me but it never works. My relationships didn’t work because I got cheated on, got dumped because I am autistic, and once abused me.
A guy at my former job I had a crush on. He is a school maintenance. He seems like a nice dude, good looking, but he kept flirting with another coworker who is averaged height and they got together. He said he liked her since he first saw her a year ago. He is like I think 6’6” and she looked about 5’4”. So not fair. I got jealous seeing them but didn’t show it and said I am happy for them. I’ll never find someone.
Like the guys that like me (including one of my guy friends I’ve known since 4th or 5th grade) I don’t want them.