Well,being involve in someone's relationship as a friend is so far from my being coz I'm still young for it but I do have an advice for them...
"If u,ur bf and ur bf's ex are all on the same campus or surroundings don't worry about ur bf coz maybe he already moved on from the past. Even though they both love each other so much on the past but it doesn't mean that he can't give u his luv or he's whole heart unlike on the past, maybe he can give you more than the love he gave. And if he's willing to marry you or if he's saying that you're his future wife put ur trust on him. coz if he doesn't love you then he'll not announce it all over the world..
I don't know what I'm saying coz I never experienced this so forgive me if this is not true..