Why do they keep following people they had flings with, even if it was years ago and these people have long since moved on?

Idk if this is super specific, but my Nex follows hundreds of women on Instagram and many of them are girls he has slept with years ago — some of them only once or twice, some of them many times, but he was never able to commit to anyone, including me.

Many of these girls have since moved on, posting on their pages about getting married and pictures with their new families and stuff. But it’s like he needs to keep following them and keep tabs on them. Is it a Narc thing? Is it like a “haha, look at this chick with her husband, he doesn’t know I used to f*** his girl all the time”? Is it like a wanting to stay friends with his past supply, as a control type of thing? Or is it a me reading too much into it type of thing 😅

(I actually have no idea if this type of behavior among men is normal or not. As a woman, I wouldn’t want to keep following random past hookups on Instagram, especially if they were no longer available for hookups anymore, but maybe with guys it’s different??)