Is he entertaining her?

This is going to sound so childish and insecure but oh well....

I’ve been dating this guy for a few months and a month ago this girl commented “that smile😍” under one of his pics . No big deal but I ask about it he says that was his ex he went to her prom and they dated a few years. She’s the ONLY girl that’s still posted on his page and the only guy posted on his page even tho that was 5 years ago. I ask if they still talk and he’s like yea a lil bit but I told her about us and her commenting and she’s gonna respect our relationship. I’m like ok. So yesterday he posts a pic of him and his mom and she comments “I see where you get your smile from 😍” so at this point ....idk what to do. Yea yea it’s just Facebook or it’s just a comment🙄don’t help he liking her half naked pics online . She’s definitely not commenting without being entertained cuz his other ex just liked the pic and kept it moving ... what do I do?

I shouldn’t have to talk to her myself to find out .