I'm sorry things are so complicated.
Have you talked to him about your intention to come out to your family soon? Not in the sense of "all the cool kids are doin' it, so why don't you come out, too?
" but rather in the sense of "this is a big step for me and I just wanted to let you know
." And see what happens.
Understand that this might terrify him, BTW, because you coming out might make him feel that he should confront his own feelings in the matter, about his girlfriend, about you, and about his denial about his own sexuality.
Or it might make things better. He might be able to see that it's a good idea to come out and be done with the secrecy. He might even learn that his girlfriend has suspected this all along, I might add.
I hope things work out for you. But in the meantime, good on ya for having the courage to come out.