You know, when I think about it, those parents of theirs really deserve a lot of the blame too.
Not that Marie wasn't being a shitty person helping things along, but them directly inflicting such misery on both their kids really doesn't reflect well on them.
I believe in the original novel they straight up kicked Leon out after mistaking him for being gay. They were the ones that spoiled Marie rotten (Leon helped a little with this one), and by basically forcing her to drop out of college, they put her on track for the rest of her life.
By every account, they failed both their children and took the high road for it. Her garbage taste in men is still her own fault, but having friends in college would have made a big difference.