I scrolled through a few of the other comments just for more context and I have to say I’m leaning toward you having a small, casual conversation with his friend and telling her to tone it down a little

You’ve said that the comments range from calling you an “adonis” to saying stuff like “who needs mountains when there’s a natural wonder right here” (referring to him) and giving heart eyes. Idk I mean I have a brother and have had male friends who I view as brothers and I definitely wouldn’t say that kind of stuff to them. I know some people are more naturally affectionate and nobody in this situation is doing anything wrong but I think if it really makes your gf feel weird it would be worth talking to the friend and saying “hey I love you and value our friendship but sometimes your comments on IG can be a little over the top and I don’t really want anyone to get the wrong idea since I’m in a relationship”

You said in another comment that it doesn’t really make you uncomfortable but if it does then that’s worth mentioning because obviously your feelings matter