WAIT I think I know some but probably not what you're going for. I do want a love triangle where the asshole is a competitor but loses badly to the nice one.
Not a love triangle but he didn't go with his shit ex:
http://www.mangago.me/read-manga/ore_to_joushi_no_kakushikoto/
Also chooses the main guy instead of shit ex, seme is a closet gay while uke is out with trust issues cuz of ex:
http://www.mangago.me/read-manga/tonari_no_usotsuki_suzaka_shina/
Uke had past abusive boyfriends, sticks with the sweet one:
http://www.mangago.me/read-manga/kore_wa_kitto_yume_no_naka_no_kiss/
http://www.mangago.me/read-manga/suki_kamo/
ok i just found this and skipped to ch4 and i think he goes for the nice one
ok but what if both semes are assholes. and, hear me out, the uke gets with BOTH of them LOl
http://www.mangago.me/read-manga/sakaku_opera/
I'm surprised no one mentioned Hate Mate http://www.mangago.me/read-manga/hate_mate/
HAHAHAHAHA!! CAN YOU PLEASE RECOMMEND WITH SOME LOVE TRIANGLE YAOI? BUT THE THING IS THE UKE CHOOSE THE RIGHT PERSON (The kind one not the Asshole one) ( ̄∇ ̄")
I'M DAMN TIRED OF THE STUPID UKE WHO FALLS FOR THE ASSHOLE SEME ヽ(`Д´)ノ
THANKS!