Just stop going. It's fairly simple. Your girlfriend could go either way. Either she shows that she loves an organization/idea more than you and she sticks with them. Do you really want someone to share your life with that does not love YOU but loves WHO YOU PRETEND TO BE. Or she has doubts herself or sees how you're being treated after you leave and she leaves herself, you'll have each other then to help and support and it makes for a really good love story.
Trust me, I have made the mistake twice in my life, being married twice and currently going through my second divorce. The JW's love their organization more than they will ever love you and they will use it against you at every twist and turn. If she's an engrained JW she won't think twice to turn your ass over to the elders and she will backstab you along the way. That's what my current wife is doing even though she doesn't know what she's doing herself.
So walk away, there's plenty of fish in the sea. It's going to be hard and tough as it is.
Also, resentment from an ex is always going to be there. I don't think it's healthy to stay with someone for more than ~5 years unless you're really a soulmate. The fact that you're not going to share the same goals and ideas about it (even if you stay with the JW's, you'll always have doubts) will cause MUCH trouble and within 5 years you're going to feel even more stuck than now, probably thinking about your future and when you should leave with a little one on your lap (again, I speak out of experience).
Think about the future:
You stay in, you get the girl, you are miserable, within a couple of years you leave anyway and not only will she resent you even more, you'll have kids and/or a second family to worry about too.
You leave now, you have a 50/50 chance at the girl, you are happy, within a couple of years you may have the same girl or someone else, she will either not resent you or you won't know if she does, you may have kids and a second family but you'll be able to celebrate christmas with them and have a general good time.