I believe that when MC started making advances towards Bella, he only thought that he had to deal with an absent husband who neglected his own wife.
Bella having a dead preteen son is very depressing. A mentally ill wife, a broken husband and a dead child? That is certainly more than MC signed up for.
If I were in MC's shoes, I would feel incapable of building anything alongside a woman who has suffered so much in life. I don't believe that anyone can be happy after losing so much.
Isn't there a line in game about if the MC knew then what he knew now he'd have stayed well clear... Or something similar? Or am I making that up. Anyway I'm sure it's been hinted at that bells past is more than just her husband leaving.