Yes, but most of the people I've come across can't play out a bisexual character properly. Most of the time they use the term bisexual as a excuse to have characters who have canonically expressed interested in the opposite start seeking a same-sex relationship, without having to explain this drastic change in sexual orientation.

Ether way, every single time I've seen someone play a character as "bisexual", that character has never expressed any interest in the opposite sex in-game.