http://www.mangago.me/read-manga/aishuu/ (kinda..)
http://www.mangago.me/read-manga/koi_wa_koi_o_shiru/
http://www.mangago.me/read-manga/overdose/
http://www.mangago.me/read-manga/ubawareru_koto_marugoto_zenbu/
http://www.mangago.me/read-manga/ore_ni_koi_shite_dousunda/ (i think it fits...)
http://www.mangago.me/read-manga/koi_ga_bokura_wo_yurusu_hani/ (warning: twisted :)
(●'◡'●)ノ
http://www.mangago.me/read-manga/waltz_with_a_black_cat/
http://www.mangago.me/read-manga/yachin_hanbun_no_ibasho_desu/
http://www.mangago.me/read-manga/mukizu_ja_irarenee/
http://www.mangago.me/read-manga/warui_yume/
http://www.mangago.me/read-manga/koi_no_tsumeato/
http://www.mangago.me/read-manga/aishuu/
http://www.mangago.me/read-manga/michi_dzure/
http://www.mangago.me/read-manga/neji_no_kaiten/
http://www.mangago.me/read-manga/kedamono_nanbiki/
http://www.mangago.me/read-manga/when_a_man_loves_a_man/
http://www.mangago.me/read-manga/scarlet/
http://www.mangago.me/read-manga/chime_peach_na_seito_to_banana_na_kyoushi/
Mangas about cheating?