my frnd 18f is in a relationship with her coaching sir, he is the one who proposed her!!

i dont know how to feel, the moment she told me about him, i have been feeling very uneasy about their relationship.
well today me, her and other 2 guy frnds went to book fair. while the guys were busy i cornered her and asked her directly abt her bf (her insta stories were obvious that she had a bf).

at first she resisted because of his 'name'. further persuasion she told me he is a muslim thats why she was resisting. i told her its okay to have a muslim bf.

like no problem, but then i asked her if he was a classmate, she bursted out laughing. i was confused. she told me he was 7yrs older than her. i told her its okay to date someone 7yrs older as she was 18 above too.

but then she told me "its my physics sir, jiska class karke aayi hoon". i was dumbfounded. maine bola WTF why are you dating your teacher its not good.

wo boli ki kya prblm hai? he is the one who proposed me.

i could not form words. how can a teacher propose their student? wo khud karti toh maan liya jata but sir???
abhi realisation hua why she specially brought a 'heart red velvet' cake just for her sir's bday

one of the guy frnd is my bestfrnd too and for her he is like a brother figure. a very protective one too. last time she busted his dating life to his teachers and he is waiting for her to date so he can take revenge (we are all same age).
but if he hears abt this he will srsly take action against the teacher obviously before informing her parents.
she requested me not to tell him strictly.

i m very confused and disturbed. she looked happy with him but what they were doing was hell wrong.

def its not a crime she is 18 and can date whomever she wants to and i should not even care because its not my business but...

just wanted this off my chest, i cant even tell my other frnds

i want to tell my bestf and her parents but samne uska jee main and neet hai and mujhe lagta hai iski wajah se it can hamper her studies.