We're shacked up, can we attend church?

I have been with my girlfriend for 3 years. We live together and have not always believed as Christians. Over the past year we have studied and started believing. I was raised in church and so was she. I love her and want to ask her to marry me. I am saving for a ring. We have discussed going to church but don't feel like we would be accepted since we are not married and I have a son from another relationship. I would like to find a good church to attend and get married there. What should we do? Do we need to go to the courthouse and get married so we can go to church?