Why do I keep attracting frenemies as friends?

So from about age 19 until now, it seems as if all the close friends I've made have either betrayed me or turned into frenemies.. well, except for my cousin who I've never had any issues with. One friend was nice to my face then slept with my boyfriend, another friend was really nice and supportive at first and then started putting me down all the time in front of guys and posting ugly photos of me. Another friend would compete with me for the guys I liked even though she had a boyfriend. This always happens it seems, they're really nice and lovely at first and we start off good friends and then they do something out of nowhere behind my back.

I've tried my best to be a good friend to people, but I keep being let down. I know that I'm probably the common denominator in all of this but I really can't think of what I could be doing to warrant these failed friendships and this behaviour. Is it the kind of people I'm choosing as friends? Or are a lot of people just like this towards each other?

Why do I keep attracting frenemies as friends?
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