After creation, certain angels married human women.
We have previously established that, in the Bible, the term "sons of God" refers to GOD's heavenly creatures, including angels.
The Bible tells us that, several generations after creation, as the human population increased, certain angels lusted after beautiful human women, left their assigned heavenly roles, and married them.
1 Now it came to pass that men began to exist in great numbers on the earth, and daughters were born to them. 2 So when the sons of God saw the daughters of men were beautiful, they took wives for themselves of all they chose.
(Genesis 6:1-2 OSB)
These angels sinned by stepping outside the role that GOD had given them to marry.
Apparently, it was GOD's will that angels remain celibate and single. When certain Jewish religious leaders tried to trap Jesus regarding the resurrection, they asked Him a question about marriage after the resurrection.
23 At the resurrection whose wife will she be, since the seven [brothers] were married to her?”
24 Jesus replied, “Are you not in error because you do not know the Scriptures or the power of God? 25 When the dead rise, they will neither marry nor be given in marriage; they will be like the angels in heaven.
(Mark 12:23-25 NIV)
As a result of their sins, GOD punished these angels, imprisoning them in darkness.
The apostle Peter wrote:
4 For if God did not spare angels when they sinned, but cast them into [Tartarus] and committed them to pits of darkness, held for judgment; 5 and did not spare the ancient world, but protected Noah, a preacher of righteousness, with seven others, when He brought a flood upon the world of the ungodly; 6 and if He condemned the cities of Sodom and Gomorrah to destruction by reducing them to ashes, having made them an example of what is coming for the ungodly; 7 and if He rescued righteous Lot, who was oppressed by the perverted conduct of unscrupulous people 8 (for by what he saw and heard that righteous man, while living among them, felt his righteous soul tormented day after day by their lawless deeds), 9 then the Lord knows how to rescue the godly from a trial, and to keep the unrighteous under punishment for the day of judgment, 10 and especially those who indulge the flesh in its corrupt passion, and despise authority.
(2 Peter 2:4-10 NASB)
Likewise, Jude wrote:
5 ... I want to remind you that the Lord at one time delivered his people out of Egypt, but later destroyed those who did not believe. 6 And the angels who did not keep their positions of authority but abandoned their proper dwelling—these he has kept in darkness, bound with everlasting chains for judgment on the great Day.
(Jude 5b-6 NIV)
These angels' choice to abandoned GOD's designed order and do what they wanted to do (sin) had massive negative consequences.