What is he doing?

My ex-broke up with me about a month ago, just the other day he said he wanted me back. I told him I already have a boyfriend and week should keep the feeling mutual... We both agreed, but now he's acting like a jerk to me. He's going back to our old ways, and he's calling me a slut or something similar and then saying "jk" . Its really pissing me off because he's giving me too many mixed signals. I told him I was going to the library , and sure enough, he was there, but I missed him. What does this mean?
What is he doing?
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