Under Catholic teaching, there are many types of mortal sin that would prevent someone from being in the state of grace necessary to receive Holy Communion. These include the sexual sins of fornication, adultery, homosexual actions, use of artificial contraception, and civil remarriage after a divorce without an annulment.However, Peters emphasized that the law only deals with “gravely wrong public behavior” and not cases where a priest must “read souls.” Obtaining a same-sex marriage license is both gravely wrong and public, he said.
If two unmarried people (of any combination of sexes) share the same address, seem to stick together and show up in church, the pastor may suspect a sexual aspect to exist in their relationship but he would not know unless they confess it. If they are involved sexually and still come to Communion, they commit a grave sin but outwardly there is no scandal: the sin remains private; the priest does not aggravate the situation by allowing them to Communion since he "cannot read souls".
If the same couple make a public act that makes their sexual involvement a publicly known fact, then the priest must not allow them communion because otherwise he, the priest, would be contributing to a scandal for the Church.
It is said sometimes that a private sin excommunicates by itself, whereas a public and obstinate sin requires a formal excommunication in order to not only rescue the sinner but also to avoid additional sin of giving scandal.
Thank-you. I suppose it is usually easier for us. Most parishes are pretty much “the village” and we all tend to know each other’s situations. Even if we don’t as lay people, the priest knows. But again, our parishes tend to be small and very close knit, though even in big parishes it is expected that someone attending regularly will register and part of that process is social and religious history so the priest will know. I once watched a young fellow strut into church with his very pregnant, then girlfriend now wife, on his arm. At the appropriate time he approached for communion and the priest refused him. Saw a priest do it to an openly gay couple once also. I honestly don’t think “gay marriage”, licensed or otherwise has anything to do with it for us. Marriage is a sacrament of The Church. Everything else is at best adultery.