Naughty, naughty ... just remember "what goes around, comes around". What would you do IF you found out he was seeing another woman, or better yet, if you came home and he had a desire for some "muff pie" ... would you let him munch your muffin then without telling him? Imagine how you would feel if you started to give him a BJ and noticed the scent of another woman's pussy on it!
...I imagine even us straight guys, who love going down on women, have 'devoured another man's porridge every now and then, BUT, a fresh cream pie is very distinguishable. If he's not bi, it probably wouldn't go well if he determined you had another man's cum inside you. Maybe its time to suggest 3-somes, both MMF and MFF ... they're fun.