My girlfriend and I are each others' firsts (first s/o, first kiss, first fuck) but she's still friends with this one guy back in high school that she had a thing for. Recently she found out that he liked her back then, too. He moved away now and they only talk online rarely now, but the idea that she and him could have been together just gets under my skin.

It's with other guys, too. Casual remarks about other dudes looking good cause a pang of uneasiness that takes a while to shake off. My girl's told me multiple times that she's perfectly happy with me and thinks cheating is disgusting, having known lots of men who cheated on her family. I really have no reason to distrust her.

Is this just insecurity? I know I'm being incredibly childish here but how do I tame this green-eyed monster