I don't think I've met anyone who would attend pride that would have any issue with him getting engaged to this girl.
They'd probably cheer.
Pride isn't about gays as much as people think, yes, a lot of the LGBTQ+ folks show up with their gender and sexual preferences basically hanging out in the open for all to see, and that's the point. Everyone I've talked to is all about being proud of who you are. Straight, gay, bi, lesbian, trans, queer, whatever. Be you. Pride is more about being who you are without prejudice, not some anti straight LGBTQ+ rave.
This guy could have proposed in the middle of the main stage at pride and gotten cheers from people.
Sir, your proposal didn't defeat shit. Good luck in your future.