<human>: We used to go out years ago while working, broke up, we managed to stay friend after a rough patch and everything was swell since. 

We always had some feelings left for each other even after all that time, especially when we were such close friends throughout.

The fire was kept at low heat and had increased lately on my side, she's not reciprocating at my level and it's making things really hard for me. 

Lately while I was on a trip she got a number from the other coworker that replaced me for that time so they can communicate if one gets sick or late. 

It threw me on such a jealousy spiral!
I always saw myself as a very stable guy with minimal mood swings but this sent me on a loop affecting every aspect of my life, feels like it's numbing me, crippling! 

She said she hasn't been talking to him about private stuff and that it's only been done on the work phone but still the thought of it driving me nuts, the guy is someone I helped/help a lot and she's been my friend for so long, I told her that if they do talk she should let me know because I'd like to back away from any connection with them.

Can you condense the text into three sentences or less?
<bot>: She's not interested in me, even with some feelings for me, I am interested in her more than her,  it drives me nuts  and I work with her.  What should I do?