Good job, man. You’re doing the right thing despite the pain you feel. Unite your pain with Christ’s suffering which he underwent so that you might know the truth and enter his Father’s kingdom. Keep pursuing your faith. Listen to Catholic Answers Live, spend time with the Blessed Sacrament and never neglect your prayer life.
I was not as smart as you. I reverted just as my now-wife and I got engaged. She has never been religious and tried RCIA but decided to stop and is now firm that she will never be Catholic. We haven’t been blessed with kids yet, but She cannot stand that I must pass on my faith to our children and she feels forced. We have been married just 2 years and have sought counseling but still talk of separation and the “D” word. I try to think that God gave me this cross because I can handle it but the weight is unbearable sometimes. I would wholeheartedly suggest that you reach an agreement on this matter before you get more serious with your girlfriend.
Best of luck, you will be in my prayers.