I've just split with my DP, so my DC are likely to have a step-parent at some point, as I was to EXDSS. The main issue which will arise is how EXDP manages the relationship and integrates them all.
I'm grieving for the fracture of what I thought was our nuclear family, however I don't regret leaving him for a second, knowing the emotional abuse EXDP put me through, after the carrot he dangled through our 7 years together.
EXDP also expected me to take care of the majority of both house and child matters, despite us both having full-time jobs, mine being more demanding as it's at a much senior level.
I'd love my DC to have a SM like I initially started off as with DSS. Someone similar to a kind aunt, who shares good and bad times, and is able to discipline them in the same way as she would her own DC.
The trouble is I'm certain EXDP would expect the same heavy lifting from her, that he expected from me, except now he has 3 DC who will be SDC, instead of just 1. Looking back I can see that's where my resentment kicked in, and withdrawal of help taken for granted began. EXDP isn't introspective enough to examine his own behaviour during the relationship, so the cycle is likely to continue.