Senpai has his own story in another manga-
Name - Kooporasu E Youkoso(in chapter 3.5)
Aww it's very healthy relationship I don't get why it has such a low rating may be cuz seme is not seme type much he is much of a air head , can't help at least things turn out great at the end and especially that senpai helped them lot to get their relationship together .
Soshite Koi ni Naru