I'm almost always up for sex 99.9 percent of the time and on the rare occasion I am not into sex because I might be feeling tired, we usually masturbate together to porn or a shared fantasy...
Since we also share a girlfriend, We have sex so often either with her or together that he doesn't mind a day off here or there on the rare occasion I am really not feeling sexual.
I think whatever works for you, works for you, I don't see any problem with taking it for the team... if he is also interested in doing so by getting you off when he may not be feeling sexual himself.