Gem....feelings of jelousy are the most powerful of human emotions. That is why is is called the "green-eyed monster". I felt it, one time...and, I can tell you that it literally made me sick. I saw my recently separated "boyfriend" with his new squeeze...and, I pulled my car into a parking place...opened the door..and vomited!!
That was decades ago....I now, cannot imagine what I saw in him....lol....
By the way...just for the record...I was prettier than her, smarter than her, more interesting than her, more loyal than her......
Mother Nature is responsible for the intensity of this kind of emotion. It helps to propogate our species (bonding, hormones and all).....
Fortunately, you are stable enough and smart enough to keep far away from them.
This will pass...just give it some time and keep facing forward.....
dandylion