I knew he was a Jehovah witness when I agreed to be his girlfriend
As soon as I read this line I knew pretty much how the rest of the story would go. That's not an insult to you, it's just that those of us who've had personal experience with this religion know how these things work.
Unfortunately, you didn't know, and so you got hurt. You were collateral damage in the Watchtower's war against anyone who refuses to bow to its leaders.
I know your feelings are raw right now, you're confused, and you're frustrated. You have every right to feel this way. But there are a couple things you need to know.
This may sound odd to hear it, but in all honesty you don't want him to just up today and decide to quit the religion and be with you. The problem with this cult, or any cult, is the indoctrination runs deep. And if he quits "for you" he WILL end up holding it against you in his mind somewhere, and it WILL come to the surface at some point and cause problems. If he is to leave, it absolutely must be because he has come to terms with the true sadistic, nefarious, damaging, and insidious nature of this religion and has made up his own mind that he must leave.
Unfortunately there is no way to predict whether that will be soon, years from now, or never. Depending on how closed-minded he is it may be possible at some point to share information you have learned, but only if he's able to hear and never being pushy. If you attempt to push it will backfire. Period. It absolutely will backfire.
It would be difficult for you, but your only real option (if you want a relationship of any kind with him) at this point is to make sure he understands you are available as a friend. Be someone who is a safe place for him to talk to. Listen if he expresses doubts and support him in researching those doubts. But refrain from "putting your two cents in". Just be the safe place where his mind knows it can try to crunch through the things that deep in his psyche he knows are wrong but his religion has trained him to suppress. In time he may wake up.
But you may very well never be together as a couple again, and if you're going to go through with all this then you need to be ok with that or you're only setting yourself up for more hurt.
If you're not ok with that, then you should cut your losses and move on with life.
My intention is not to be harsh, but to just be realistic with you.