Most people think of an emotional or physical relationship with someone other than their spouse. While this is true it is not the only form of adultery.
Matthew 16:4
Adultery is the mentality in the heart of preferring others, or money or goods or political parties over God. God hates that anyone or anything would take priority over Him.
In a marriage it is a form of adultery when a spouse prefers their parent or siblings or other family members above their spouse. When one spouse is disregarded by the other spouse in favor of extended family, then the spouse is preferring, in an adulterous affair against the other spouse.
I have heard it said that a man was having an emotionally adulterous affair with someone they are not sleeping with but enjoyed their company more than the company of their wife.
There probably was adultery in their heart in the preference for this woman just as there is an emotional connection of a husband or wife toward their own families over and above their husband or wife.
Whenever someone prefers an extended family member over their spouse they are committing adultery in that partiality toward the extended family member.
When our allegiance s spread beyond our spouse in a preferential way it is a form of adultery, causing the spouse to feel unloved and abandoned.
Our spouses should always take priority over any extended family or business partner or friend outside the marriage relationship.
When a wife feels left set aside as the husband prefers his family over her nurture then he is neglecting his wife. This is true also if it is the wife preferring her family over the spouse.
Just because someone is not sharing a bed with someone does not mean their allegiance and attention are proper. It is one thing to be friends with the opposite gender, and quiet another to prefer that friend over our own spouse.
There are some people who will pay more attention to and enjoy others outside the marriage relationship while neglecting to show that same attention to their spouse. Narcissists often do this, they will attend strongly to the desires of others while negating the desires of their spouse.
We do not have a physical relationship with God, it is Spiritual and lovely and He does not want us to prefer any person over Him. When push comes to shove we must always take our side with God.
When someone is treating our spouse disrespectfully we must always take the side of our spouse, never the side of the one who abuses.
Many marriages are ruined by extended family who attempt to divide our allegiance with our spouse to prefer them. This is devilish and the people that do it must be removed from the relationship.
No one should be allowed to come between or be superior to our spouses.
Genesis 2:24
“Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh”
If there is anyone in extended family or in business or any other relationship who causes adultery in our hearts to divide our marriage devotion, they must be removed.
I have seen marriage relationship in which one spouse will join with the extended family against their spouse to be accepted by the group, this is sin and destructive to the marriage.
Leaving family when we get married is the best way to develop our own oneness to each other. Remaining with family while under the family's influence will destroy or delay the development of a strong marriage bond.
The Lord took us away from family for career reasons when we were first married and it was the best thing that could have happened to us. When we came back to family years later is when the problems began to emerge when family attempted to insert themselves into our marriage without knowing anything about the dynamics of our relationship.
Then once again God removed us as we moved across the country for career reasons, helping us to return to the marriage we had when we first left. It is very rare that extended family supports and encourages a marriage to build their own traditions, choices and closeness to one another.
Too many people in a marriage relationship is more likely to ruin the closeness than it is to develop it.
Closeness comes when two people depend on God first and then one another without interference from those who love to judge, dominate and influence one spouse over the other.
God said to "leave and clever" for a reason, He wanted the couple to grow in their own oneness without interference from those who do not understand the dynamics of the couple or their personal desires. Working things out together without the opinions of a "group-think" will cause emotional and Spiritual growth for a strong marriage.
Genesis 2:23-24 "… 23 And the man said: “This is now bone of my bones and flesh of my flesh; she shall be called ‘woman,’ for out of man she was taken.” 24 For this reason a man will leave his father and mother and be united to his wife, and they will become one flesh."
No one else in the extended family should be inserting themselves into another couple's marriage.
Proverbs 2:17
"who abandons the partner of her youth and forgets the covenant of her God."
Preferring the companionship of others outside the marriage relationship is a form of spousal abandonment. It carries with it a greater pain than physical abuse because it is unseen to anyone but the one who has been abandoned, this one who feels deserted and without protection, left in loneliness because of the emotional and spiritual adultery of the one who places family above their spouse.
Just because someone is not committing physical or emotional adultery as we think of it do not think it is alright to place others above the marriage.