whois
Wow, I think this thread more than any has reconfirmed my thoughts that I would never get with a man who has kids. Opening yourself up to a whole world of pain.
"She's not your daughter"
"She only has one mum and that's not you"
Wow. Fuck that. So a step mum is supposed to treat husbands kids the same as any she might have, pay towards their care, run around after them, love them, but fuck that nasty cow if she dares to feel like she's doing a 'mum' role.
Unfortunately, because I acknowledge that it's a very tricky relationship to negotiate, your post highlights one of the problems - who is 'expecting' this behaviour of a step mum? It isn't the kids, who are generally quite nonplussed about sharing their dad with someone new and have to muddle through with whatever situation the adults in their lives have decided upon.
The mothers would probably rather there was nobody else in their children's lives too - I'm sure not many people become parents expecting to split up and remarry - so although it may be the way things work out, expecting someone to be pleased that you get to spend time with their children is possibly a little too much to ask unless the dust has well and truly settled and everyone's lives have moved on happily. Bear in mind there doesn't have to be another woman involved for a mother to feel betrayed by the break up of a relationship so in a scenario where the split has been acrimonious, the chances of some residual resentment bubbling under are fairly high.
Also, very few step-mothers take on the role for the children's sake - they do it because they want to be with the man they love, and although feelings may grow towards his children, and they may go on to have a really deep relationship, they are very much a 'part of the package' in terms of the basis of their relationship.
As I say, it's difficult and I'm not sure I can do it, but to be anything close to a mother, you have to accept all the facets of your role, still loving the kids when they show no appreciation, loving them because you can't help it rather than because anyone 'expects' you to and trying to ignore the times when it feels like a thankless task in favour of doing all those things because you want the best for them even if nobody says 'thank-you'.