I'd say he's Pansexual. In the past he's been with both men and women and joked about flipping so many men he had a move called the skillet (hysterical) but I'd say those days are behind him with his new job and hew love.
Semi bisexual is literally straight. And while it is a thing, it’s mainly used by straight people who want to be apart of the community although they aren’t. And also he obviously isn’t straight. He is clearly on the multisexual spectrum. And m-spec people are still allowed to have straight relationships while still being queer. I believe he is omni because he seems to have a strong preference for women.
Guys Lucifer was clearly referring to when he becomes God as; all-knowing, all-seeing and all-powerful. He was not in any way referring to his sexuality.
He was referring to omnipotent, omnipresent and omniscient - how do I know that? Because if he meant omnisexual Chloe would’ve looked hurt and NOT smile bashfully as he said it