Most bittersweet mangas I know are not very sexual:
http://www.mangago.me/read-manga/bokurani_matsuwaru_etc/ (kyuugou is wonderful at pulling at the heartstrings, this one is the fairly tame compared to her others ones)
http://www.mangago.me/read-manga/castle_mango/ (an emotional manga, not so much tragic or bittersweet, but has a somewhat similar feel to that of Link)
http://www.mangago.me/read-manga/fubin_bl/ (first story, seems a bit fast paced but has a nice bittersweet ending to it)
http://www.mangago.me/read-manga/ake_nure_goyou_ni_furu_yuki_wa/ (first story, ends at first in a bittersweet manner, but has an extra at the end that does end more happy)
http://www.mangago.me/read-manga/cut/ (has abuse, but not done by the main character to the other, but by others)
maybe try Mion's list:
http://www.mangago.me/home/mangalist/880/
Does anyone know some real hardcore tragedy bittersweet manga (any sexual genre)? I'm not really looking for abusive here, more like emotional stuff. Something like Link. Thanks!