Would I be selfish to ask my older boyfriend for an open relationship?

Hi everyone, I (19F) am still dating my boyfriend M(34) although I’ve been interested in a friend (M20) of mine.

My boyfriend is quite supportive and wise which I love about him although I sometimes dislike the social stigma we get when we’re out together so I don’t like to do as much in public with him. I know I shouldn’t care but I sadly do and I know it upsets him but I still love him and enjoy the age gap we have in private.

With my friend closer to my age we go out a lot together and he’s at the same uni as I am so it’s more socially acceptable. I would like to have him as a friends with benefit whilst still having my older more secure partner and was wondering how I should bring this up to my partner without sounding completely selfish. Any advice?