My boyfriend like his ex's pictures on facebook?

[zOmBiE.FrEaK.NikKi]

I don't want to sound like a complete strict girlfriend that tells her boyfriend what to do but it really hurts to see my boyfriend liking other girls pictures on facebook, some of the girls include his ex's.
Im fine with him being friends with them on fb but i don't see why he feels the need to like their pictures.
my boyfriend calls me beautiful and tells me that he loves me and stuff and for a minute ill believe it but when he likes another girls picture i feel ugly and really bad about myself.
i don't know, maybe im just insecure cause i can be a lot of the time and im not very confident with myself. but i dont know, i just want to know if im overreacting or if im just being silly and insecure :/

We've been seeing eachother for a year