It’s about who you love, not just who you have sex with. Two women who are asexual (don’t experience much in the way of sexual pleasure) who have a long term committed romantic relationship may not technically be “homosexual”, but they are definitely seen and treated as such. And I think the term “gay” very comfortably applies.

You can have sexual orientation without ever having sex. For example you can be heterosexual and never find a sexual partner - that doesn’t make you asexual, you’re just a heterosexual virgin.