I think you just aren't guaranteed to know that you'll get a nice step parent. My son has had two extremes (just being in the middle would have been lovely!)
My husband is DS's step dad. We met when DS was 2, moved in all together about 18 months later. He's great, tbh I read a lot of SP posts on here and think actually DS has an Angel as a step dad
. He treats both of our children (DS 1&2) as absolute equals, there's no debate over "he's your responsibility" etc, and even when DS had a few issues aged 8-10 with anger - and took a lot out on DH - DH took it all in his stride. Never once felt it was unfair, he was a child who needed support, and he got it.
They have a brilliant relationship. DS is now 17, contact with his Dad has always been there - but he's never been particularly hands on. Even his Dad has often commented how lucky DS is to have DH. He really is. I had no expectation DH would be such a fantastic SD, I just expected him to accept that DS and I came as a package, but he has gone above and beyond.
DS's ex step mother (from age 4-11) was a pretty nasty piece of work. Was brutally honest - even to his face
- how much of a hassle he was, how him being there ruined her perfect family weekends. I'm afraid in this case I will use the thing that a lot of SM's hate people saying on here - She knew exactly what she was getting into, and should have walked away if she couldn't manage EOW with DS.
As with DH, I didn't expect her to be a mother to DS, but being nice to him would have been my hope, sadly she was far from that.
The sad thing is the damage which has been done to DS and his Dads relationship, that never got over it (his Dad stood back and watched it all happen
)
Our children are now into their teens, and I have no expectation we will separate, but if we did I wouldn't plan to meet anyone new until they are both adults as I couldn't risk another step parent like that.