Hey ladies I need a little advice..

My bf is from TO but he moved here just over a year ago. Recently I've been noticing on fb that he has been liking a lot of this one girls photos. She's from TO and I guess they used to hang out. But what bothers me is the kind of pictures it is that she posts that he's liking. There's like gym photos of her in training bras and yoga pants, showing off her butt and trying to make stupid sexy faces. It just really annoyed me that he'd like so many of her photos.

So I guess what I'm wondering is if I should just casually bring her up and see if what he says, or just let it be..

Any advice would be great, Thanks!