Pro tip: He doesn't and won't.
Heterosexual means HETEROSEXUAL. That means male who is sexually attracted to women ONLY.
We can't change you; you therefore can't change us.
If a man engages in a homosexual act with another male, he is no longer straight and never was. In the old days back in the late 70s we called this The Straight Paradox. Nothing's changed.
Date other gay men and stop the thirst.
Actually he is the only one who can declare his sexuality, and even
then he doesn't owe an explanation. In the same way that some lesbians
who like both genders but overwhelmingly prefer woman over men still
call themselves lesbians, straight people can call themselves straight
if they prefer the opposite gender over the same gender. I identify as
straight woman although I am attracted to some androgynous-looking
girls, but it's not enough to want to date them or want to do it with
them. I identify as straight or maybe even hetero-flexible lol. I don't
even know, but the point is that I am the only one who decides it. If I
had sex with a woman tomorrow I could still say I'm straight. Sorry, I
know that might be a hard thing to accept.