Although you love her, you identify yourself as a Christian. You have already given your heart to God, and have said YES! to Jesus. You have two options: Turn from God, which essentially means denying Jesus is who he said he was and flushing your faith down the toilet. I don't think this will happen though, because when you first started to believe, the Spirit entered you and even if you do go through with conversion, it will always be on your heart/conscience and you won't ever be a true muslim. This is always going to be an issue. A Christian is WHO you are, not the "religion" you choose. Its not like changing shoes.
If you b) Turn from her, there will be a world of pain. But God will be pleased. Who is your #1? Where in the Bible does it say that God's purpose is that we all live happy lives, full of the things we want? This is going to be horrible for you, but you must leave her- or at least stand your ground in your faith and invite her to get to know the God you know. If she doesn't/can't, then its the end of that.
Read what the Bible says about getting married to a non believer. Its not a good basis for a marriage. This is desires of the flesh. Welcome to walking in obedience. :)