Or not.  Most Catholics don't experience any loss of union with God for most of the grave sins promulgated by the Church as such, especially those having to do with remarriage.  That the Catechism repeats the same errors is of no consequence.  See Garry Wills book Why Priests? for more about how the Church is proof texting Corinthians badly.  If you want to authoritatively refute him, you had better speak biblical Greek as well as he does.