Any mangas where the main character (uke please) knows he is being used or is a replacement or the seme cheats on him but still goes along with it either because he really loves the uke or because he is lonely/depressed... you get the idea
loves the seme*
http://www.mangago.me/read-manga/soko_ni_suwaru_na/
http://www.mangago.me/read-manga/empty_heart/ http://www.mangago.me/read-manga/zense_to_gense_to_kimi_to_ore/
http://www.mangago.me/read-manga/koujitsuei_no_tobira/ http://www.mangago.me/read-manga/kimi_ga_koi_ni_midareru/ http://www.mangago.me/read-manga/ai_ga_kami_wo_korosu_toki/
Any mangas where the main character (uke please) knows he is being used or is a replacement or the seme cheats on him but still goes along with it either because he really loves the uke or because he is lonely/depressed... you get the idea