Would you ask him why?

I told my boyfriend of 7 years awhile ago that this guy that used to be his acquaintance commented on how nice my butt was to one of his friends while I was in another room and touched my boob pretending like he was fixing my bra and how it made me uncomfortable. He did this while I was in a relationship with my boyfriend. My boyfriend seemed upset about him doing that. But just now I saw that my boyfriend followed him on Instagram a couple of days ago. That guy is not following him back. It kind of upsets me that my boyfriend would follow a guy on Instagram that I said made me uncomfortable and was trying to get with me while I was in a relationship with him. Would you ask him why?