Congrats on getting confirmed! I was confirmed last night as well!
I’ve been exactly where you are. Here is my advice, follow Our Lord, He is leading you. Pray about it and just tell her how you feel. Stand your ground (she will respect that). Most importantly, be prepared to tell her why.
After almost 3 years of dating, my girlfriend (now fiancée) and I were not living chastely at all. She was a lapsed Catholic at the time, and would periodically make comments that she didn’t think we were living right by God’s eyes (she was right).
I started looking into the Church Christmas of 2012. I told her that I couldn’t keep on as we were. She agreed. Well, then things got hard. We fought about it a lot for about two months. I stood my ground on the issue. Then, we got through it and it wasn’t a big deal anymore. We both wanted to be chaste and we did it. She went to confession and I went when I was received into the church. We had to break out of a cycle of serious sin but God has so richly blessed us now.
We are now long distance. A few months ago, I told her that even though we’d been completely chaste for over a year, I no longer thought it was ok for us to sleep in the same bed when I’d come to visit. She talked to her Priest about it. He said it might not be a near occasion to sin for us, given that we were so committed to chastity and the unique situation. I still told her I felt it was wrong (scandal, etc). She loves me and she was willing to go along with this for me even though she thought I was probably overacting. I now stay elsewhere when I visit.
In our culture chastity is made out to be impossible. Once you try it, you realize it is hard but it makes you appreciate marriage so much more. All of a sudden, all the Church’s teachings on sexuality make sense. Our relationship has completely taken off since we’ve brought God into it. We are closer than ever and so excited about the big day (May 24!).
Bottom line, tell her how you feel and why. It will be hard. But, if she is right for you, the two of you will adjust and I promise it will change your life for the better. Once you start down this road, constant prayer is required. You will need Our Lord’s help to stay strong.