Damn me and my playing-a-woman ways! I never knew!Jade Empire was one of my favorites.
It was also the only Bioware game where they allowed you to romance both the main women sidekicks so successfully, you get a three-way. Even Dragon Age, in which both women were slutty as fuck, never let you romance/sleep with both at the same time.
(The Isabella/Zevran/Leiliana/Warden four-way does not count, since it never involves Morrigan)