Infidelity is an act; it is a verb. There are several types of Infidelity, but this will focus from a Christian point of view: the breaking of an oath, pledge, or covenant. The root of this word has been in the media, of late; however, this violation has been committed going back to the Garden.
Infidelity in the Word: it comes from the word - infidel. It is being unfaithful, faithless, unbelieving, incredulous, without trust in GOD.
It is awful when a leader of a family get caught up in this violation. If the family can't trust their leader, neither can our Creator. In many places today, this can result in the death-penalty.
2Cor.6:5 is a great question for Fake-Christians, and Hypocrite-Leaders! "What concord[agreement] has Christ Jesus with Belial? Belial = another name for Satan, Sons[Kenites, Tares] of Satan, worthless, wicked. Now re-read the question! The answer is None, not, 0.
2Cor.6:14-16 is concerning being unequally yoked with unbelievers. Not a big deal? It is currently getting ignorant-Christians killed around the world. Never stand on a lie. Deception is bondage.
The beginning of Knowledge starts with reverencing the LORD. The beginning of safe-guarding one's self and family, starts with reverencing the LORD.
"Trust in the LORD with ALL thy heart[mind]. All means that there is no room for "Another-......" Jn.3:16 Believeth on HIM, shall not perish." Rom.10:9 "Believe in thy heart[mind], and confess with thy mouth." Ti.5:8 Worse than an Infidel?" Being "harvested" by Satan!
The Religious ones are "seeking to Save their own souls - and, will, lose."