Presumably, your boyfriend is being baptized in the Catholic Church because the Church does not recognize Mormon baptism. That means you would be his godmother. A godparent is supposed to be a spiritual mentor to a godchild, and to be a role model in living a Catholic life. While there is no law preventing someone from marrying his godmother, it is imprudent for any number of reasons for a Catholic to be a godparent to someone she plans to marry. I can only recommend that your boyfriend ask his pastor to recommend someone else to stand as his sponsor for baptism.
