Following girls?

Okay so I may sound insecure ( and trust me I’ve really been working on this) but whenever my boyfriend follows women on Instagram or likes a photo of a female, I get very triggered. The girls he follows happen to only be women he knew from highschool. I’ve seen him like photos of girls who used to go to his highschool too, but the photos were never inappropriate.. more like just normal selfies or pictures. He doesn’t follow or like pics of any models or famous girls on Instagram. He’s 20 (graduated in 2020) and I’m 19 (graduated in 2021). He always tells me he is only into me and he doesn’t look at other women sexually but for some reason I can’t help but wonder why this is such an issue for me. I think I just assume if he follows the girls he is into them? Or that he must think they’re hot or something if he likes a girls photo? I honestly hate saying that because it sounds childish but I’m just being real. He is the only serious relationship I’ve been in. We’ve been together since freshman year. I never tell him anything about it, I just keep to myself really. I don’t let it bother me but when I see a girl on Instagram he happens to follow, or see a photo he liked, for a split second I feel anxiety. It isn’t something that is ruining our relationship, but I think it’s just something that only affects me.

Does anyone have advice or a personal experience to help me out on this personal issue? I’m too afraid to speak to anyone close to me about this so I hope someone on here can help.