Could it have ended differently?

For those of you who didn’t finish Mansfield Park, I’ll summarize part of it. Henry Crawford decides that he wants to work his charms on Fanny, but ends up falling in love with her and proposing. She tries to turn him down because she’s actually in love with Edmund. Henry thinks he just needs to prove to her that he will remain constant in his love. He’s inspired by her goodness and even becomes better because of her influence.
However, he fails in his constancy. While visiting London, he and Maria begin a flirtation and end up running away together. Mary Crawford scandalizes Edmund by expressing her regret, not that Henry could do such a thing, but that he would be so reckless as to get caught. She believes that if Fanny would have accepted Henry’s offer Fanny “would have been the making of him” and this never would have happened.

I’ve been thinking about this a lot. Would Henry have remained faithful to Fanny, or was it inevitable that he would stray? If he had been constant, would he have made Fanny happy? Is it fair to ask women to "be the making of" men? This is the part that bothers me. Obviously we won't marry men who are doing drugs, unfaithful, etc. But we also believe in the Atonement and people's ability to change. So how do we judge correctly?
I guess the reality is that women can make good men better. The operative word is "good". We don't have to bind ourselves to morally corrupt men, with the hope that they will improve. But we can take good men--men who honor their priesthood--and help them become better.

And does anybody else have a hard time with Edmund and Fanny? It's just seems like such an older brother/sister relationship. He acts so superior to her through the whole thing.