Welcome back! There is a great celebration going on in heaven because of your return and one going on here too. Obviously, it is important to find and associate with a good group of fellow believers so that you can hold each other accountable. The deceiver is not just going to let you go so you will need a strong support group to help you keep moving in the right direction.
As far as your GF goes, Paul addresses this issue in 1 Cor 7 where he writes,
[SUP]12 [/SUP]To the rest I say this (I, not the Lord): If any brother has a wife who is not a believer and she is willing to live with him, he must not divorce her. [SUP]13 [/SUP]And if a woman has a husband who is not a believer and he is willing to live with her, she must not divorce him. [SUP]14 [/SUP]For the unbelieving husband has been sanctified through his wife, and the unbelieving wife has been sanctified through her believing husband. Otherwise your children would be unclean, but as it is, they are holy.
[SUP]15 [/SUP]But if the unbeliever leaves, let it be so. The brother or the sister is not bound in such circumstances; God has called us to live in peace. [SUP]16 [/SUP]How do you know, wife, whether you will save your husband? Or, how do you know, husband, whether you will save your wife?
Even though she's not your wife (yet?), I think it is still an appropriate passage. And, as an atheist, she is going to be watching you like a hawk, waiting for you to mess up or to find a chink in your armor. Be strong in your faith. Do this by being a good person. Do this by walking in the light of Christ. Do this by being that two-legged living gospel. Who knows? Maybe she will desire to have that same inner joy that true believers tend to exude. Maybe God put you in her life for just this very reason. Paul also talks about this earlier in 1 Cor when he writes,
"5What then is Apollos? And what is Paul? They are servants through whom you believed, as the Lord has assigned to each his role. 6I planted the seed and Apollos watered it, but God made it grow. 7So neither he who plants nor he who waters is anything, but only God, who makes things grow. 8He who plants and he who waters are one in purpose, and each will be rewarded according to his own labor. 9For we are God’s fellow workers; you are God’s field, God’s building."
So don't worry about trying to convert your GF or to actively try to change her mind. Plant the seed by acting in the ways of Jesus, water the seed by being strong and steadfast in your faith, and let God provide the growth in her (if that's His will).
