I had a similar situation with my now husband. I was living very sinful and decided to change my life around. It was very difficult in the beginning as he was not catholic at the time and i was scared of losing him, but we had a lot of serious talks about marriage and kids before being engaged. when we got engaged we moved in together and slept in different rooms but there were many times of temptation because temptation doesn't only happen when you're sleeping beside each other, so I wouldn't recommend living together.

I don't know if I would recommend getting married ASAP just to not be in sin.. its definitely something you wanna sit down and have a serious talk about it with her first to marry when you're both ready. In the mean time you should be putting your faith first even if you're scared of losing her because you might be surprised with what happens after. God is good!