<human>: We were together for around 11 months and he broke up with me in February (he didn't really tell me why). 

After two months of no contact, we bumped into each other on campus and we ended up spending the day together and sleeping together. After that, we saw each other every few weeks. 

2 weeks ago, he called me and asked me to help him with an assignment he had to do for the next day because he would have been kicked out of university if he didn't do it. I stayed up with him all night and helped him with it (even through the stressed yelling) and he gave it in on time.

We spoke later that day but he suddenly seemed quite cold, like he didn't want to speak to me (even though he called me). He was the same the next few times we spoke and started saying that "this doesn't make sense" and that "we should see other people" without explaining what happened and told me he doesn't want to speak to me any more. 

Now I'm pissed at him because I feel like he used me to help him with his work (because his other friends just want to smoke his weed) and dropped me now that he got what he needed from me. And I keep thinking about reporting him to the university for cheating on that assignment (he did, he bought an essay and edited it a little) because I don't want him to think he can use me like this. 

I'm not sure where to go from here; I don't want to blackmail him into being my friend or anything, that would suck. But I'm really angry at him for being a jerk.

Summarize the given text in a few sentences.
<bot>: Ex-boyfriend pretty much immediately turns cold after I help him out with a big assignment; I kinda want revenge.