It depends on what this “past” is. Everyone has a past, and everyone's a sinner. We all have situations that have shaped the person we are. As you are getting to know each other, your main focus should be whether this person will be a partner for you to enter the kingdom, to live a life of repentance and Holy Communion. In regards to a “sinful” past, it is important that they repented and returned to God. Once we repent, we are completely cleared of our sin. This is the amazing power of the forgiveness of God, the sinner becomes a saint, the adulterer pure, the liar trustworthy.  If there are certain aspects of their past that you are concerned with, you should discuss it with them. Also regarding specific rules and rites, it is advised to speak with your confessional father. He can give you guidance on this matter and give you a clearer answer.