I... kinda agree with the mom on this one. Hear me out, How would you like if the girl your son is dating is also dating his friend. I would feel angry and disappointed. She won't be there to give him her full love or devotion. But, i'm against her on the basis that he can't marry the one he likes.
I may make jokes you don't like. If that is the case, stop reading my comments and get over it.
Spoiler!
Yes, that was a joke.