I don't know how long you've been together but you said a long time. Any serious relationship demands some level of mutual decision making especially with something big like this. Should she support your decision? Sure. But you can't control her reaction to such an abrupt change to your relationship. You've been living as if you were married for so long and now you are causing a sudden rift in that. Her reaction is completely understandable and you would do well to give her the space to get it out and to be heard. That is IF you want to preserve the relationship. Maybe you don't and that's okay too. Just don't make her feel stupid, shamed, inferior for not being as enthusiastic as you.
...to informing her we would have to get separate places...
LOL. You informed her. That's a great example of a one-sided decision. Sure it's ultimately your decision to make but you're in a relationship and this decision drastically effects that relationship. She deserves to be in on it.
As for your zeal. I'm no priest and certainly no spiritual father of any sorts. But I converted 20 years ago as a young man and did the exact. same. thing. It's okay to want to be chaste but it's going to take a lifetime. Nothing you do now is going to get you there overnight. So frankly... chill out. I mean look at what you wrote...
...but then again I am trying to do things for my salvation.
Oh YOU are the one doing the saving? What about the Lord??
...Lust is something that has had a stranglehold...
This shows me your faith is weak and needs time to strengthen.
I'll tell you one thing that works wonders for all this: Marriage. I don't know the details of your circumstances but I can't help but think you need to marry this girl soon. I struggled with the idea that in one moment it's not okay for me to be having sex with this woman who I love but somewhere in the marriage ceremony it suddenly becomes okay. And not just okay, but a crucial part of the marriage! Because one aspect of marriage is that it's a mutual agreement to use the relationship as THE vehicle for salvation. It has a way of taking all this and transforming it for good.
God bless you, my friend! Good strength! Welcome to the family! Go easy on that girl and yourself.