Why are (some) people being so condescending towards the OP, and even quite nasty?! 'You sound so young,' and 'grow up!' and 'he's saving her pics for wank fodder,' and 'unless you're 13 why do you care about a snapstory?' and 'are you sixth formers?' etc...
I am not 'young' and I would be pissed off with this; my DH taking - and saving photos of another woman, and keeping them on his phone. Pretending he is just taking pics in the pub but conveniently getting her on them.
Someone said 'would it bother you if she wasn't pretty?' but the boyfriend wouldn't be arsed with her if she wasn't 🙄 As a pp said, he wants to be associated with her because loads of men fancy her. (Coz she's very attractive.)
@Kathrinebubble YANBU, this is not acceptable, and your boyfriend is being an arsehole. Sadly, he probably won't change, so it's up to you to decide if you can put up with a man who lusts after and leers over other women he fancies, and doesn't give a shit about your feelings.
Personally, I know what I would do in your situation. Dump his ass. You're worth more than this.