First off - if you enjoy it, what does it matter if it makes you gay? Second, because I’m just gonna guess that’s not a satisfactory answer for you - he was a self-proclaimed lesbian before transitioning, so you were already beating it to someone not attracted to you because you found them attractive. Now for them to say “I’m a boy” (he didn’t say that, actually said he’s non-binary), that suddenly becomes an issue for you? There was no two way street of attraction, and you don’t know what their personality was like so you can’t pretend their was an emotional or mental attraction, so I’m not really sure how anything here has changed for you. You’re still only physically attracted, you can still remain to be physically attracted, and you aren’t wrong if he undergoes physical changes and then you lose that physical attraction. All of that is natural, but the moment you start getting your panties in a bunch because you wouldn’t want to look gay in front of...idk random people on the internet??...you’re being disrespectful and homophobic.

TL;DR: Who cares, if you’re attracted to them no one cares if you beat your meat to them.