ah crap...
I guess he never got a good explanation as to why she didn't want to marry him, and he still thinks it's because he wasn't "good enough". So now that he's successful and has proven himself, he wants to try again.
Sorry Stand, but it has nothing to do with you as a person and everything to do with the fact that you are related to each other. There is no way to change her mind. Even if she wasn't now happily married to someone else.