I want my mom to break up with her boyfriend
Do you think she is better off without him?
No, I just think she should stop seeing him.
If you don't have a legitimate reason they should break up like domestic violence or cheating then you should mind your own business. Children should not have a say on who their parents should date.
She's old enough to know what she's doing.
Exactly, so there is no need for you to interfere. Let her make her own choice on who to date.