Rolling my eyes hard with this. Was so painfully fucking obvious this is the route it would go. He will date this girl, the mom will keep getting advances by this dude from work. She'll cave in to try and move on whether she bangs the guy or not, then they'll both start realizing they are miserable with their current partners and then get together by the end (unless they do the less used route where the kid grows up and actually finds someone his age and the mom has to deal with it. I think I've only read like two other manga that does this and the rest do what I said at the beginning). So damn original.