Many of these men know they have totally unresolved issues relating to that first family - they aren’t actually ok with being a nonresident parent, with the children having a different, main home, with being the secondary parental influence on their children, with having to pay maintenance, and so on.
But they also know that will put a new partner off. So they hide it (and often the circumstances help them to do so). Even where the new partner has children herself, she probably hasn’t in any way anticipated what she’s getting herself into. Why would you expect that? And then there’s the superimposition of the guilt on to her. He gets to take on a poor victim, martyr of his first family’s demise.
One of the biggest differences between the experiences of stepmothers and stepfathers is that resident parents (predominantly mothers) don’t so often operate out of fear that their children will be ‘taken away’ from them. They are much more secure in their parental role and are able to have a stepfather come in and give him reasonable levels of authority in what becomes his home. Stepmothers assume the same will happen to them, and find themselves down a guilt-ridden, Disney dad rabbit hole in which they are always available to take on the role of antagonist (for everyone!). Add in a whole load of societal gender roles shit and you’ve got a much more difficult situation which makes it harder to form any kind of positive step parenting relationship.
Sometimes, it seems that getting (re)married and/or having a baby together triggers a lot of this stuff. It was ok and he was a better parent, but actually committing to the stepmother seems to precipitate all the worst aspects of stepfamily dynamics. It might be that shift comes from the man or is prompted by how the external actors around the marriage/second family respond.
But it’s not uncommon for there to be a big shift, often just at the moment when the stepmother actually needs support. And for that shift to position the stepmother and her child(ren) as problems. Rather than being able to feel secure in her new marriage, she finds herself almost punished for her husband’s guilt over moving on. Rather than being able to feel that her husband is her partner and coparenting, raising their new baby together, she (and the new child) are treated as threats to the first family children and she finds herself having to fight to protect herself and her child from the man she thought was her partner in very tangible ways. Over an over again.
Nothing breeds resentment like that kind of situation. Feeling like you have to fight your husband just to be a normal parent to your child is awful. Birthdays and
christmases become fraught because you can’t so much as buy your child a present without it being positions as a sleight on the SC. The anxiety over your family buying anything for your child makes this even worse. In some of the cases on here we see even trying to buy your toddler an ice cream at the park becomes fraught with tension.
No one anticipates this. It’s completely weird and, of course, they didn’t get married and have a baby with the expectation that they’d spend the whole marriage/child’s life feeling like they are in hostage negotiations over the most ordinary things.