Girl's Behavior

Why can't I let this person go?

There is this girl I used to eye ball at the gym all the time purposely (flirtatiously). I did it for the longest time because i started to really like her. I had a feeling she was already taken but wasn't sure. This went on for well over a year. She always seemed to notice but never really showed interest back. One day I noticed she started to get what i thought was a baby bump. Turns out it was. I knew she was already taken at that point but since i'm stupid and pumped up on testosterone after working out I still felt ballsy enough to eye ball her to the point where she would notice. She always seemed to enjoy it but never really showed interest back. One day like a year and a half later, long after she had this baby, I decided I had enough of going to the gym everyday and eye banging this girl I know is married (I found out over time) and that I clearly would get rejected if I asked her out. So i decided to completely let it go, go in the gym and ignore her (not eye banging her all day) and just focus completely on my workout and that ONLY. I was tired of not getting the gains I wanted (even though i still worked hard in that gym). After that, I noticed a sudden shift in her behavior around me. She and her friend would be eye balling me everyday and staring at me and giggling when I walked by, which actually annoyed me because I knew both of them were married with kids and I felt she just liked attention. She and her friend did this for months everyday. I seen them eye banging me from across the gym and stuff. Just felt like this tension but I was already over it. Not completely though. I still would slip up and do it back but not very much. But anyway... months go by and they eventually stop as well. Sometimes I will still see a stare or two come my way. What really annoys me is i see her work out with some guy now which I know isn't her husband but i can't help but to feel this internal jealousy that makes me want to knock him out lol. Why can't i let this go?
Why can't I let this person go?
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