I read this manga. I don't remember much but it was about cheating seme (he was doing it on purpose). Uke was forgiving but one day he saw nails' marks on the seme's back and got mad. I'm not sure but they had a friend that uke went to when he got mad at seme. I have been looking for it for a long time. Please help!
PS. Sorry for my English :)
I believe you are looking for chapter 6 of the manga Yachin Hanbun No Ibasho Desu
http://www.mangago.zone/read-manga/yachin_hanbun_no_ibasho_desu/mf/v01/c006/1/
I feel like it's just the silent before the storm. But... OMG, Sangwoo's words at the end of ch 37 was... I don't kown how to say it. Everything now is so calm and in some way kinda cute that I'm affraid what happens next. If only peace in ch 37 could last...
ikr same here ify ╥﹏╥