I guess the ethics of it is simple.
Sex is sex.
Better a blow job then wanking it yourself.
Is hetrosexuality simply about sex? IMO I do not think so.
Where you dip your wick is irrelevant to whom you are emotionally attached too.
I am gay because I love other men not just because I have sex with them.
I have had sex with a handful of women but do not label myself bi nor straight.
It just happened. They were there. I was in need. It was fulfiled.
They are straight because they love women not just to have sex with.
So in the end if he gets off and you have fun getting him off why try and label it?
It is simply hormonal and sexual.
Danger is when you start to think it is love and it is merely lust.