New Situation - Same Panic

Good Morning All,

I am hoping somebody can offer me some clarity here. I've been struggling with this horrible feeling of jealousy for the past couple days. What is triggering it is that I dated a new guy last year for a couple of months. It ended not horribly but he put the nail in the relationship and friendship. My issue is we work together and I see him flirting with other people all the time. It turns my stomach. While I can see what a masher he is and how I should have listened to the not dating advice I got here initially because obviously I couldn't see him clearly. I am getting that anxious nautious feeling again when I see him and these giggling girls. Is this old feelings about exn? Is he an N too? I'm just confused - don't want to care and definitely don't want to be so affected by him and his women mongering. I'm also a bit embarrassed I fell for the B.S. in the first place! So...any suggestions? Thanks. xoxo - BtrflyGrl.