This. A lot of the times the guy bails.
My mum was a single mother for majority of her life (my grand parents helped a lot).
So, depending what the woman is like and her past then possibly. If the kids are a pain than that would be a nono. That said, most times, if you are the step-father/mother you will get frustrated for the first few years until the kids grow on you.
I sure wasn't nice to my step-dad until I was 14-15 (started living with him at 11 when I moved to the UK).