What would you do if your SO had a child with someone else while you was together but you already have a child together?

Lets say they got drunk and cheated, or it was while you guys was talking but not official, or maybe you broke it off for the night and they went and slept with someone else. But in any situation the other chick ended up pregnant by your SO and you are pregnant by them too or already have a child together. Would you

A) break up and not have anything to do with said child of other woman

B) break up but still keep in touch with the mother so your children can get to know their sibling

C) stay together but not have anything to do with child of other woman

D) stay together and let the children get to know each other