+1. It drives the plot forward, giving a reason for the wife to leave the husband, which I'm assuming is going to happen at some point, and the MC isn't dating the wife's sister, so there's no hint of NTR there at all. If you want to change it, fine, but you shouldn't feel compelled to do so. Some people are fragile and will complain about everything, but if you cater too much to them, you'll end up with a story that's shallow and boring.