It happens in Ch- 21.1
http://www.mangago.me/read-manga/seashell_boy_pearl_cum_boy/uu/iur_chapter-21.1/pg-1/
Damn that's quite specific but sorry, I haven't encountered sth like that yet.
Idk if this is similar but here we have two ppl doing it beside a corpse. It's psychological and interesting tbh
http://www.mangago.me/read-manga/blind_play/
Can you recommend some yaoi manga manhua/hwa that fucking next to sleeping guy?