Fruits Basket!
One of the funniest and saddest mangas i know, with a happy ending, and almost every character has a sad backstory
Theyre looking for yaoi
ok some of my fav's
http://www.mangago.me/read-manga/aiso_tsukashi/ (uke: prison, prost., bad parents)
http://www.mangago.me/read-manga/koi_no_mannaka/ (both: lonlyness, bad parents)
http://www.mangago.me/read-manga/abiru_junjou/ (uke: abondoned by mom, bullied from classmates)
http://www.mangago.me/read-manga/hanazono_no_kioku/ (seme - but I don't want to spoiler)
http://www.mangago.me/read-manga/sagatte_omachi_kudasai/ (uke: very afraight guy, doesnt like to be touched- find the reason in his past)
uh oh - I love this one! not really bad background (ok, single mom) but the 'slice of life'...
http://www.mangago.me/read-manga/castle_mango/
if you want- I collected all of them and more in a lil list
http://www.mangago.me/home/mangalist/104732/?filter=&page=1
one thing I prefer with a story with a sad past is how he or both he and the partner deal with it in order to obtain their happy ending. and that's what my list is about
http://www.mangago.me/home/mangalist/72757/
So this story connects with Renai rubi no tadashi furikata so you can either start with Renai first or with the extra
Extra about his past: http://www.mangago.me/read-manga/azami/
His story starts on ch 4 but feel free to start from the beginning: http://www.mangago.me/read-manga/renai_rubi_no_tadashii_furikata/
Continuation of his story in Renai but about him only now. No other couple: http://www.mangago.me/read-manga/hadakeru_kaibutsu/
First if you want I tagged the mangas I enjoyed:
http://www.mangago.me/people/tag/179149/Tragic+Past%2FAbusive+Family+%E2%9A%AB/
Plus that one, from chp 4 on, it's centered on the butler Miyauchi, prepare yourself to cry a river... (omegaverse)
http://www.mangago.me/read-manga/kashikomarimashita_destiny/
I'm looking for a yaoi with a sad backstory or that has a character with a sad lifestory or who's life is for some reason hard. could be anything really - sickness, grew up without parents, the character is poor or is just overworked, recovering from something, is or was raped, involved with mafia - ANYTHING GOES
the only thing that is important - PLZ NO TRAGEDY ENDINGS! the story HAS to have a happy ending. it can be an ongoing manga too, I'll just hope it ends on a good note.