HOW FRIENDLY OR CLOSE SHOULD YOUR PARTNER AND HIS BABY'S MOTHER BE? CAN THEY BE BEST FRIENDS?

I'm on a relationship with someone who already has a baby mother, we just had our baby a couple of months ago and a month after his baby mother first found out that i was pregnant she got pregnant too month later apparently unplanned could this have been subconsiously planned? She is in a relationship with the father of her new baby but close with my partner the father of their son. do you think they are in competition? Or we are the fix it relationships for them. I have nightmares and can't sleep constantly about the depth of their previous relationship and it now as he doesn't like to talk about their relationship and they broke up because they were more like best friends and not in love. Does this mean their relationship is unresolved and their may be possible feelings for each other still? also does this mean our relationship os going to be a shamble when we have to share the children in different homes, i'm worried about the consequences of them been brought up differently and it causing arguments?