Because jinyao swapped their sperm. Yiyun thought that Rourou is his kid until Jinyao appears and claim custody for rourou that's why he was there when Rourou growing up
But to begin with, why yiyun was there? I mean about the sperm and whatnot, he want a child of his own too?
He wants too. And his mother wants him to get married to have a grandchild but he has no plan on getting married and all his blindates are a failure so his friend A helped him. It was shown around the first few chapter.
Ohhh okay that makes sense. Thank youuuu
I'm still confused on to why Yi yun was there since Rourou's birth ╥﹏╥