http://www.mangago.me/read-manga/sabaku_no_harem/
http://www.mangago.me/read-manga/akatsuki_no_yona/
http://www.mangago.me/read-manga/baby_kokoro_no_mama_ni/
http://www.mangago.me/read- http://www.mangago.me/read-manga/kawaii_hito_saitou_ken/manga/boukyaku_no_shirushi_to_hime/
http://www.mangago.me/read-manga/shinomiya_kun_no_sekai_ga_owatte_mo/
http://www.mangago.me/read-manga/futari_no_renai_shoka/
http://www.mangago.me/read-manga/itsuka_kimitachi_mo_otona_ni_naru/
No love triangle:
http://www.mangago.me/read-manga/beast_master/
http://www.mangago.me/read-manga/dengeki_daisy/
http://www.mangago.me/read-manga/karekano/
Not shoujo but feels shoujo/no triangle:
http://www.mangago.me/read-manga/14_sai_no_koi/
http://www.mangago.me/read-manga/chibi_vampire/
Occasional rivals but no real triangle/the main couple is obvious:
http://www.mangago.me/read-manga/usotsuki_lily/
http://www.mangago.me/read-manga/kimi_ni_todoke/
http://www.mangago.me/read-manga/lovely_complex/
http://www.mangago.me/read-manga/tsubaki_chou_lonely_planet/ (possibly?)
http://www.mangago.me/read-manga/mars_souryo_fuyumi/
http://www.mangago.me/read-manga/high_school_debut/
http://www.mangago.me/read-manga/ookami_shoujo_to_kuro_ouji/
The third list basically has no love triangle plot but there might be a rival here or there. But they are not long lasting like say..Vampire Knight.
Thank You !!! (●'◡'●)ﾉ
Can someone recommend shoujo manga list with no love triangle plot. Thanks :)