What's up with him?

So I dated this guy and had a great time with him but I got scared and started backing out and so he ended up ending it, understandably. That was over a year ago. after we broke up he stuck around. I got the idea that he regretted his decision but he never acted on it, then i got sick and he was the first person i went to which ended up in us having sex, he got abit over excited and since that night he has been strange around me. Sometimes ignoring me and sometimes making it clear we have a history. During the summer I had to work with him for 3 weeks and I had iniatially had asked him if we could talk before that because i didn't want to end up with an awkward situation but he avoided that chat until we were on location and even then he wasn't keen. While working together he'd sometimes be sweet and talk to me like there was nothing wrong and then he'd ignore me unless i did something wrong and other times he'd be irritable/angry with me or do things to get me angry. One evening he was flirting with another colleague (who he knew was taken) infront of me and the next morning it was as if it never happened. When we did chat he obsessed about the fact that he didn't want to give me the wrong idea and thats why he was ignoring me. I have never asked him to come back because even though i miss him, he needs to make that choice on his own which is why i dont understand why he was obsessing about not wanting me. I dont understand why he is so up and down. What is happening here? why is he obsessing about not wanting me when i have never asked him to come back or if he wanted me.
What's up with him?
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