Paul gives practical relationship advice in 1 Corinthians 7. To singles, he advises to stay single if you can. Marriage undercuts your ability to serve God wholly. Get married if you wish. To married couples, he teaches to have sex and lots of it, stay together even if it’s rocky and don’t leave and remarry. To spiritually mismatched couples, Paul writes to stay together if it spiritually benefits your spouse and kids. If you are left by your unbelieving partner, you are free to remarry.