Anger towards ex

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Some background info:
>date ex for a little less than a year
>he dumps me because he says that he's not emotionally stable enough to date a girl
>I understand and somewhat agree, but I'm still heartbroken
>we hook up for about 3 months after the official break up
>it was really more than hooking up, we were essentially dating without the title
>he starts distancing himself and tells me he wants to stop hooking up
>I ask why
>he gives me a bs answer
>a few weeks later he tells me a female friend likes him, but the feeling isn't mutual
>at this point, we aren't hooking up and are barely even friends
>a week after that he backtracks and tells me he does like her
>I remind him of the reason we broke up, because he "can't date anyone right now"
>he reassures me that they will never date
>he starts getting involved with her
>I find out they're officially dating a couple weeks later

This is just one example of how I got absolutely played for the fool I am during this relationship. I've finally realized that this guy was just no good. Hindsight is 20/20 and it's pitiful that it took me this long to figure it out.
Regardless, I am so damn bitter and resentful because of all this. I still see him occasionally because we have shared friends. Simply seeing him puts me in a foul mood because I start thinking about how pissed I am at him. I've tried to just avoid him (and therefore my anger) in general, but that just amplifies my animosity when I do finally interact with him. It's the kind of rage and frustration that can make you cry.

Tl;dr how can I get over my resentment towards my ex?