My boyfriend likes other girls nudes online

My boyfriend of 10 months is following this girl on Instagram, she used to go the his school and she posts half naked pictures of herself. So, they definitely know each other personally. There was this one picture of her straddling her bed in a bra, playing with the strap. He was one of the 26 people to like the picture, and it was posted 3 weeks ago. Should I confront him about it, or is that me being too over protective?