My husband needs to know why his past marriage can keep me from becoming Catholic. He’s at least thinking about the annulment now but has some questions. He’s having a problem with the Church possibly not allowing me to become a member because of him. If someone can give him an explanation, he would feel better about the annulment process.
Your husband’s past marriage does not prevent you from becoming Catholic, if you agree to live as brother and sister. But, because the Church must presume that his previous marriage is valid until declared otherwise by a marriage tribunal, the Church presumes that your current marriage is invalid unless and until an annulment is granted. For those who are married, a valid marriage is a prerequisite for being received into the Church, unless those involved in a marriage that must be presumed invalid agree to observe the celibate chastity required of those presumed not to be married to each other.
Annulments and the Catholic Church** by Edward Peters