I want my so to cut someone out of their life
Can you tell me the reason you want them to cut someone out of their life?
It might sound shallow but I just don't like them
I'm sorry you are feeling that way. It is rude to expect someone to get rid of a friend for your benefit. Maybe you should talk to him about it if it is bothering you that much.
I don't know why they won't take my advice. I may be young but I'm always right.
You might be right about some things but cutting someone out is really hard. And depending on how long this person was with your so, then it might be even more difficult. Give your so time and he might follow your advice.