All This Could Have Been Avoided! **SPOILERS**
If Fanny was mature enough to have sex, get pregnant, contemplate marriage to another man to cover up the pre-marital sex and pregnancy, she should have been mature enough to write Marius and tell him about the situation. I am not blaming Fanny for being left pregnant and alone and I understand times were different back then but she should have told him. Fanny played too many games with Marius. I had no problem with her breaking up with him so that he could fulfill his dream of sailing, because that is something he would have always regretted, however she should have written to Marius and told him about the situation. If he told her she was on her own, then yes go marry the other man. She never gave Marius a chance to step up. If she had told him he could have made it back home from the nearest port, married her, claimed his son, and then gone back out to sea. The love interest in "Pirates of the Caribbean" made her situation work and she was only able to see William Turner every 10 years.
I know this is a fictional story but how stupid is she going to feel when Marius marries someone else, brings the woman back to the small town, has multiple babies with his wife, and Fanny has to see him in public with his new family? This situation bothers me just as much as the situation in "Legends of the Fall." In that movie the love interest was not pregnant so she had no reason to rush. If she loved the Brad Pitt character she should have waited like she said or at least she was sure he was dead or she absolutely did not love him anymore. I am o.k. with the way the love interest in "Count of Monte Cristo" handled her situation because she knew Edmond Dantes was in prison for life and more than likely never coming back and she couldn't reach him even if she wanted to.