Single parents have a duty to be responsible about who they date.
When it comes down to it, any partner who has the potential to turn into a serious relationship has to be good to the kids, as well as their parent. There are far too many horror stories relating to horrible stepparents for moms and dads in the dating pool to take their options lightly.
Unfortunately, it is very easy for people to be blinded by their rose-tinted glasses (or simply their fear of being alone) when they start dating somebody, even if the evidence suggests that they might not be a suitable match for their family. It can take something upsetting happening for them to realize that they are not making a good choice, and even then, some do not want to see reality. Breakups aren’t any less hard just because there are kids to think of as well.