First, I'm going to answer no. You're not being homophobic. But, I also think you're asking the wrong question. And most of the answers are starting with that incorrect premise.
The more important question is have you fallen for the "bury your gays" trope? It is entirely possible, and even common, to kill off LGBTQ+ characters without being motivated by bigotry. In fact, if you know the history of the trope, it actually started as a way of including these characters in stories during a time of extreme regulation. It was the time when a married couple had to have separate twin beds on TV. Being anything but cis/het was (and for many, unfortunately, still is) seen as sinful, and the powers that be that controlled publishing and production of entertainment didn't want to be seen as pushing "sin", so if you were going to include characters like that, you couldn't do it in any way that could be seen as promoting them as positive. So, easy way to avoid that was to kill them. It's the reason the virgin survives the horror films in the 80's, while the teens who have sex get killed (often while having sex).
The common questions I'm seeing in the answers are "Does this move the story along?" "Are you doing this because they're gay?" And that's too low a bar. That's like the Bechdel test - Do you have two female characters who have names and talk to each other about something other than men? Great! You're not a sexist. [insert eyeroll emoji here]
Does this death move the story along? Show me a death that doesn't. Even some random extra's death serves some purpose in a story - illustrating a danger, showing a character's cruelty, showing the limits of the hero, etc. So that's a pointless question.
Likewise "are you just doing this because they're gay?" Again not necessarily a good indication of anything. Sometimes you want your audience to empathize with the grieving partner of a gay character, so in that case your answer would be yes, you killed a character because they were gay. And it's appropriate.
I would ask these questions instead. First, does this character's death have an emotional impact on the audience? Man Eating Hot Dog's death, probably not going to make me cry. But a main character dying? That will leave an impact on the audience.
Second, is there a way to accomplish the same thing without killing them? It's easy to fall into tropes, so ask yourself is that what you've done, or is this really the best way to tell the story you want to tell.
And third, who is left? I don't want to boil telling a story down to a math equation, but a quick check might be useful. Did you just kill off over half of your LGBTQ+ characters with one death? Then maybe you want to revisit question 2 there.
There are some really great videos that go in depth into this trope that I watched recently.
So with all that (keeping in mind that I don't know more than the summary provided), I would say that you're ok. You've avoided not just homophobia, but also the trope born from it.