Given everything you’ve described, it’s understandable that you need to step back — but the core issue is your partner not taking full responsibility
A lot of step-parents feel very positive and fulfilled when they meet a partner and build a relationship with their partner’s children. However, when a new baby arrives, the dynamics shift. Your step-children shouldn’t be disadvantaged because of this change, and neither should his ex-partner.
From what you’ve described, you may be beginning to see some of the underlying reasons why your partner’s previous relationship struggled. It doesn’t sound as though there is an equal partnership around childcare, and it appears he tends to rely quite heavily on others to take on that responsibility. Some of the language you’ve used about the children and their mother is quite critical, perhaps without you realising it, and that may be affecting how you see the situation.
The affair in the past isn’t really relevant to what’s happening now. The focus needs to remain on the children’s wellbeing and on how the adults involved communicate and share responsibilities. It’s also important not to attribute the children’s behaviour solely to their mother’s parenting. Children do misbehave, and it is their father’s responsibility to manage that, rather than placing blame elsewhere.
You are part of a blended family, and it seems that both you and your partner are finding aspects of that challenging. The difficulties you’re experiencing don’t stem from the ex wife or her decisions, and she shouldn’t have to act a certain way to ensure your partner parents appropriately or contributes fairly. Your change in circumstances shouldn’t negatively impact her routine, finances, or responsibilities.
At the heart of this is the dynamic between you and your partner: how labour, parenting, and emotional load are divided, and how supported you feel. It also sounds like you may be feeling overwhelmed by the number of children in your care, and that you would prefer more clarity around when and how you are expected to
parent.
It sounds as though you’re feeling the need to step back a little, and that’s completely understandable when the demands of a blended family become overwhelming. The key question is not whether stepping back is “allowed”, but how to do so in a way that is fair to everyone—especially the children.
Ultimately, the real solution lies in their father taking full responsibility for his own children. That will require effort, consistency, and some difficult adjustments on his part. It’s something he should have already been doing, rather than you having to initiate this conversation.
What lies ahead is likely to be challenging and will require honesty and commitment from him. But it’s important that you are not carrying the emotional and practical load for decisions and responsibilities that aren’t yours alone.