How could one become guilty of spiritual adultery?

In a spiritual sense, adultery denotes unfaithfulness to Jehovah on the part of those who are joined to him in a covenant. Natural Israel in the Law covenant was, therefore, guilty of spiritual adultery because of false religious practices, some of which included sex-worship rites and disregard for the seventh commandment. (Jer 3:8, 9; 5:7, 8; 9:2; 13:27; 23:10; Ho 7:4) For similar reasons Jesus denounced as adulterous the generation of Jews in his day. (Mt 12:39; Mr 8:38) Likewise today, if Christians who are dedicated to Jehovah and who are in the new covenant defile themselves with the present system of things, they commit spiritual adultery.​—Jas 4:4.

The Greek noun phi·liʹa (friendship) is found only once in the Christian Greek Scriptures, where James warns that “the friendship with the world is enmity with God . . . Whoever, therefore, wants to be a friend [Gr., phiʹlos] of the world is constituting himself an enemy of God.”​—Jas 4:4.