Which side characters are gay? Aymeric and Haurchefant can be but that depends on the WoL's gender.
For the Rising event, the vendor (who is an clone of 1.0 Minfillia) says the goods are made by her wife. There's a side quest in Outer La Noscea following a... Roe and cat boy couple who were thrown out and mistreated not because they were gay, but because they were an interracial relationship. There's a male Lalafell in Camp Drybone that has a speech bubble in his dreams when you walk past him, begging Raubahn to take him and treat him like his Sultana (This one isn't gay per se but more queer in general)
Those are the only explicit examples I can think of. There's a lot more subtext based stuff when you come to things like the Scions that is then also dependent on your WoL's gender