try checking this list if you hasn't read it yet (=・ω・=)
http://www.mangago.me/home/mangalist/12765/
http://www.mangago.me/home/mangalist/25771/
give these a go :)
http://www.mangago.me/read-manga/koimonogatari/
http://www.mangago.me/read-manga/hidamari_ga_kikoeru/
http://www.mangago.me/read-manga/haikei_niisan_sama/
http://www.mangago.me/read-manga/hana_wa_saku_ka/
http://www.mangago.me/read-manga/yuuutsu_na_asa/
http://www.mangago.me/read-manga/itoshi_no_nekokke/
http://www.mangago.me/read-manga/blue_sky_complex/
http://www.mangago.me/read-manga/hana_no_mizo_shiru/
http://www.mangago.me/read-manga/sayonara_itoshi_no_my_friend/
http://www.mangago.me/read-manga/slow_starter_ichikawa_kei/
http://www.mangago.me/read-manga/500_nen_no_itonami/
http://www.mangago.me/read-manga/hana_no_miyako_de/
Not something tragic, but something deep that makes you sigh at how beautiful their love for each other is (not just smut)