Most Helpful Girl
Let her go ! I cannot stress this and sorry to be saying this but you should not stay with someone who doesn't put you first in her life, someone who's having clearly an affaire with a student that ended up being that guy she's sleeping with and the guy who wants to marry her too? Is her only goal in life is to get married or what? Cause if thats the case i'd say maan this girl ain't your future wify, doesn't deserve to be at least.
To you it looked all good but to her one person came and changed the whole game for you 3 and now she's lying cheating and doesn't know what she feels for you or for him? She just put you and the new guy in the same level of intimacy, love, happiness, memories...
Let her go, you'll find someone else but she's not the one.
Good luck and sorry if its a bit hard. I said what i wished someone told me about my relationship looking from the outside she looks like she's been out of it for a while now