@Ffeeeff Sry, but I don't think Oto knows his ex fiance well. The fiance himself said in this chapter that he just visited him occasionally. I doubt that such rare and fleeting meetings would result in a friendship or an understanding relationship. And you can't forget that before the pregnancy Oto and the ml lived together for a month so at this point they could know the others had/good habits (contra to the ex fiance).
There is also the thing with Oto not sharing his worries be it to the ex fiance or the ml.
But I must say that even though we don't share the same opinion on the characters knowing each other I like your way of thinking logical about the childcare aspect