I don't see what's the problem with Kento. It's not like Seiji was a lot better really. Kento was an asshole but Seiji was a freaking irresponsible guy. Both were pretty much trash, but both supposedly got better at the end.
More importantly, Kento was so guilt-ridden when he came back to Shou that I don't think he would ever cheat on her again. All in all, Shou got a pretty good deal there, probably even better than Yuki.
