There are two problems here:
Firstly, you appear to be looking for excuses for your sin instead of actively excising it from your life.
Secondly, you claimed you are a Christian, and stated that she is not. Read Paul's words in 2 Corinthians 6:14 "Do not be yoked together with unbelievers."
In practical terms, that means if you are a believer in Christ, don't marry an unbeliever, and don't get into a business partnership with an unbeliever. Those are "yokes". God doesn't tell us this to limit our enjoyment of life, but to protect us from misery and hardship. Living with an unbeliever "as though married" is as much a violation of this principle as actual marriage.
Marrying an unbeliever is a surefire way to heartache. While you may love her with the strength of Christ, she can't do the same for you. She has no anchor in her worldview that makes adultery, abuse, neglect, or any other mistreatment fundamentally wrong. She can't agree with you in prayer. She can't pray for you. She has no obligation to respect you as Scripture requires her to do. She will likely (eventually) resist whatever time or money you want to give to the things of God. If you have children together, there WILL be constant tension in the home about how to raise them, and the consistent pattern is that faith loses out to convenience.
For both your sakes, don't marry her until and unless she becomes a believer in Christ with at least as much passion for Him as you have (and hopefully a whole lot more than you're currently displaying!).
As for your current situation, answer this for yourself: Who are you trying to please? Yourself? Her (or other people)? Or God?
May the Lord give you His clear guidance and conviction in this matter.
