Luke/Luca was initially a bisexual in denial
It's apparent that a lot of the users frequenting the threads on this board are making nonsensical assessments about the sexual orientation(s) of each zerophiliac.
First off, labels such as 'gay' and 'straight' are obsolete when speaking of zerophiliacs. The accurate labels that would apply to zerophiliacs are: androsexual, gynesexual, and/or bisexual.
Androsexual is a gender-neutral terminology that applies to people who are exclusively attracted to the male sex and/or gender. As you can imagine, gynesexual is the opposite gender-neutral equivalent to androsexual. Bisexual is obviously also gender-neutral terminology as well.
A zerophiliac's sexual orientation does not shift, it stays intact, and Sydney is a prime example of that. Sydney is an androsexual zerophiliac, not a straight woman and/or gay man. Calling Sydney a straight woman and/or gay man defies Sydney's zerophilia and identity as a whole. Regardless of which sex a zerophiliac presents as, s/he is still one in the same, not separate identities.
Now, when it comes to Luke/Luca's sexual orientation, people on here seem to naïvely assume that it shifts... which is very gullible to believe. Why would it shift for Luke/Luca, but not for Sydney or Max/Michelle? Because it doesn't. Be realistic.
When Luke meets Max, it's visible that Max subtly flirts with Luke. Luke doesn't openly engage in the flirting, however if you pay attention, Luke seems to go into a subtly coy, passive, and vulnerable mode when Max flirts with him. To me, that suggested an attraction to Max. It was very clear there was sensual energy going on between the two in their male forms, especially in that scene. Also, going by their body language in that scene, it's quite telling that if they copulated with each other in their male forms, that Luke would be the bottom and Max the top. This is visible by Max's dominant energy and Luke's gentle nature.
It's undeniable that Luke/Luca was simply a bisexual in denial who didn't want to accept his/her attraction to men from the very beginning. Zerophilia seemed to have enabled leeway for Luke/Luca to eventually come out and make peace with his/her's sexuality, and also gender(s).