Coming from a guy's point of view, TELL HIM!!!
Don't surprize him as everyone might end up in the morge, but hint it around to him and if the signs show positive TELLHIM!!! It is only one of the top ten goals of almost all men to get a 3 way going, but careful, although I might think about it often I would have to kill everyone involved after the fact if it ever happened but that's my personal insecurity issues I guess.