Happy Bisexual Pride! 
Xun is bisexual, while most of his relationships were with women he cares deeply for Evan who is Gay. Two women from his past return, one includes his ex-fiance Sundae Rokke who plays a major role in the story. She disappeared on him years ago and resurfaces as the president of a shady company known as A.R.E.E. Sundae's presence puts Evan and Xun's feelings to the test. Xun's other ex-girlfriend Desirée (not pictured) is an ally who encourages Xun to consider Evan feelings. Owen eventually has a crush on a girl his age and Xun gives him advice.
(the three main characters are Owen, Evan and Xun)
Similar to your vampires the god-class in the story are bisexual and also appear polyamorous. They've lived since the dawn of time so they've seen and done everything. The God class is more of a spoiler and only two make a presence in this story: (1) Mr. Patchez, later revealed to be the god of strength & hinted to be Hercules (who was known to have bisexual relationships) and (2) Viorica who serves as a guide to Owen is hinted to be Hera. She is concerned about modern man using frequency techniques to attain superhuman strength.
Other than that many in the cast are left open to interpretation Bi, pan etc. Evan has his moments flirting with some of the male characters.
