How do we deal with my son who decided to live with a woman?

Greetings in Christ, beloved brother,

By God’s grace, my family and I are doing well, striving to persevere as Christians.

I hope that you, your family, and the saints around you are generally doing well in your life in the Kingdom there in your area.

Our efforts in the Lord’s work are gradually bearing some fruit, and we are finding some hearts open to the Word.

Now I wanted to ask if you could help me with a few questions about the application of discipline in the church and in the family. I’d like to give you better news, but, for now, that’s not the case.

My son is in his early 20s and is a Christian.  For the past couple of months, he’s been living in a rented apartment with his girlfriend (a woman several years older than him, who is a single mother and has a teenage son living with them). We had spoken with both of them—and especially with our son—explaining to them the need to formalize their relationship through marriage (a covenant); otherwise, simply “living together” (cohabiting) without being married would mean living in the sin of fornication.

Since our son is a Christian and a member of the local church—a small group of Christians consisting, for now, of just four members of my family (myself, my wife, and our two adult children)—our goal has been to teach him and help him understand his moral situation. He and his girlfriend are committed to a serious relationship, but she is not yet willing to make a commitment through a marriage vow or covenant, for a couple of reasons she has given. Apparently, the main reason is that she still does not feel fully confident in my son's maturity and responsibility, and another is that, according to them, they need some time to get their financial situation in order.

When speaking with our son, we told him that whatever the reasons his girlfriend has for not being ready to enter into marriage—as God defines it (a promise or covenant, formalized before witnesses, family members, etc.)—with him, until that moment arrives (if it ever does), they do not have the right to live together as a couple.

My son has also reached an age where he wants to be independent, and we told him that was fine—it’s not a requirement that he live in our house (his parents’ house)—and that he could live in a rented room or with a friend, etc., but what would be wrong is living under the same roof with his girlfriend without first getting married. However, despite knowing these things, he moved in with his girlfriend about three months ago.

Since he has refused to repent and change his moral situation, we made it clear to him that we would have to sever our relationship with him as his brothers in Christ. He knows he can attend church meetings and Bible studies, but since the meetings are held in our own home, we told him that he cannot stay at our house after the meeting, nor can we share a meal with him, and that we cannot have “social” contact or maintain the normal family relationship we had before.

My questions are:

• Is the way we have acted toward my son—as Christians and as a family—correct?
• Since he has decided to live apart from us and be an independent son, to what extent should we withdraw from social interaction with him? In other words, does this also apply to family social activities (not church-related), such as birthdays, celebrations of special days (Mother’s Day, Father’s Day), or “Christmas” dinners, etc.?

One additional concern: since his girlfriend used to attend as a visitor but is no longer attending—by her own choice—how might this affect her, or what can we do to have a positive influence on her?

I would greatly appreciate your comments or your perspective on this matter.

May the Lord bless you in every way,