To blow or not to blow

So I love blowjobs. I have a huge oral fetish and I love giving my S.O. them (and a bunch of other stuff) but... I also have a gag reflex. Its gotten better with time and practice but I still have never made him cum without his help or changing positions. We've been having sec for 4 years, but only during the holidays when i vistited for the first 3. Now we have sex like rabbits but.. Still nope. Am i doing it wrong or is there something i could do besides stick a finger up his butt (Idk i was told thatbwouod help but he is very against that). Thanks