Why does my ex stare at me?

My ex broke up with me because he thought the relationship was not going anywhere and told me that we just had bad timing and maybe one day we could try again and things would work out better. I did not understand and was a bit angered because I felt like we could try and correct things while we had it than to just start over. He didn't give me an explanation and just blocked my number and facebook and never spoke to me again.
We both work at a haunted house together which I took a year off of so I could get over the breakup my ex was very conceited and even while we were together he'd always flirt with other girls. And I decided to work one day out of the year I took off from working at the haunt and he was acting like he was all that and being conceited and inappropriately touching other girls etc
This year I came back and my current boyfriend joined the haunted house because he's always wanted to work there. But now I always notice him staring at us, last night I was in line with my boyfriend to sign up for a room and I put my arms around him and then looked over and I saw my ex staring straight at me from the distance and it made things really awkward. Whenever I'm near my current boyfriend I always see him giving us a locked stare and when I look at him he doesn't bother looking away and it makes me feel awkward. He won't talk to me and haven't in almost 2 years so I don't know what his deal is.
Why does my ex stare at me?
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