Well then, you're SO is one lucky guy...but some men are extremely sexually active and urges can come up very often "wich are UTTERLY DISTRACTING by the way"...also, you need to understand, it is quite embarrassing to ask someone for sex + blojobs everyday.
Tell him, but I doubt that he'll always go to you to relieve his urges, it's embarassing, and sooner or later, he'll do it by himself guilt free.