i had a relationship with a non jw when i wasstill a jw, i didnt have the strenghth to leave it then, the fear won out and they kept control of me for a few years longer,
but i left eventually,
not every ones story is the same,
i would say its important WHY people leave, ie if they leave cos they cant live up to it but still believe it, then i think they are still basically under the thumb of it,
i left cos i lost my faith in it, and so will just never go back, the myth has been exposed, and however much i miss the security of it and the "community" i have seen through the myth of it all, and cant recreate it again or pretend its real,
does your boyfirend still believe it ? if so then run, cos it will have control over his darkest fears much more than you will.
if he no longer believes it as a truth then there may be some hope he will free himself,