Difficult Issue?

The decision is pretty simple. He should not go any forward with the girl. Its not about her past or her current character. Even if she reverted back and now a nice girl, it will socially be very hard for the guy to marry her while the other friend (whom she slept with) is still hanging around.

he should talk to that girl and let her know in very respectful manner that he is finding it every hard to move forward in this relationship and its not because of her past but social awkwardness. I am sure she will understand.