Can couples who live together outside of marriage receive communion?
Not too long ago, some Catholics were marked with jansenism, which thrived here and there in the 17th and 18th centuries, mostly in France and Belgium. This exacting doctrine has profoundly affected religious practice and the reception of sacraments. According to Jansenists, a Christian was rarely worthy of receiving the Eucharist.
Older Christians remember the time when the churches were full, but few went to the Communion rail. Many thought they had first to go to confession even though they had not committed any mortal sin. Of course, the Church did not teach that kind of strictness. It stressed the necessity of the state of grace, or friendship with God, in order to receive Communion. In other words, confession was required only if one had committed a mortal sin.
Today, the Church teaches the same doctrine, remembering Saint Paul's grave warning: "...whoever eats the bread or drinks the cup of the Lord unworthily sins against the body and blood of the Lord"... "He who eats and drinks without recognizing the body, eats and drinks a judgment on himself" (1 Co 11: 27-29).
People must not come to the Lord and unite themselves with Him in Communion while in a state of mind reproved by Him and the Church who speaks in His name. To cohabit before marriage is to live a life contrary to Christian teaching, a state unworthy of baptized people, a life that overlooks the riches of the sacrament of matrimony. I do not intend to judge the motives of those who live so, but their way of life does not agree with Christian doctrine.
They are not barred from going to Church. They may, they even should keep on attending Mass. They are wavering, but not lost. Mass might one day open their minds to the light of the Lord and make them grasp the grace of the sacrament of matrimony.