Bf liking a girl's photos on Instagram

We've been together almost four months and he said he wouldn't like another girl's pictures. I believed him. I went to search a friend and this one girl's profile who he follows came up as a suggestion. She was previously private. Now she is public. I saw he has liked her photos since we've started dating and previous to that would like almost every single one for over a year so I assumed they either talked or dated or something. I'm pretty annoyed he lied about it just because her profile was private. It's hurtful. I told him in the beginning of the relationship I wouldn't like other guys photos and he agreed and said he wouldn't either but now I see he has. How do I bring this up to him? I'm very annoyed.

I personally don't think you need to be liking pictures of people you previously screwed is what I'm trying to say. AND LIE ABOUT IT. So please read. Unless you all love being lied to