I think these have a similar mature feeling...
http://www.mangago.me/read-manga/bokura_ga_koi_wo_ushinau_riyuu/
http://www.mangago.me/read-manga/3_ban_sen_no_campanella/
I think these are somewhat simillar as well:
http://www.mangago.me/read-manga/koi_wo_suru_tsumori_wa_nakatta/?8AfD
http://www.mangago.me/read-manga/hitotsu_shikanai_mono/
http://www.mangago.me/read-manga/hitori_to_hitori_no_3650nichi/
Aww are there any mangas like this one? Rec me some bc it's so guddd