YA: mans finds out about sick child he didn't know about. Read in 2014.

[Sibongumusa]

I read this book in 2014. The following might not be the main story but its the plot i can remember. Couple has a sick child, husband discovers he is not the father when he is not a match, wife must look for ex. The next part the details are a bit vague but there was a suggestion of the wife and her ex having another baby so that the baby would bw able ro donate to their older sibling and the conflict begins from there