People bind themselves in to all manner of sexual impurity now and then due to many reason. For one thing they face serious issues in their lives and they cannot control themselves no more and they found themselves under the darkness of sin now and then.
They also experience sin for a long time so that they become addicted to it and they have no more the resistance to say no to it. Their spirit become so week that they lose many battles when it comes to withholding themselves always from sin. Sin, especially sexual sin, is not something one can easily get in and get out of it without paying some penalty.
Sexual immorality doesn’t usually occur overnight. First the devil weakens our spiritual awareness and the resistance to sin that is the Spirit of God in us.
Bitterness and anger have a good chance of breaking this guard against it. If one is no more walk in love, he/she has no more protection against sin that is basically the hand of God. That is because love is the dwelling place for the Holy Spirit. Hate and bitterness will drive the Spirit of God out of our lives and it opens a door for the devil.
The other thing that causes sexual sin is not living according the word of God and not reading the word of God on a regular basis. Without the Bible dictating our path in life, we are like a ship with no harbor or destination. Without the Lord speaking to us and admonishing us in his word, we are like a city without a leader and without protective gates open for the enemy any time he wishes to attack us.
In addition to that, as Christian we need to have constant fellowship with the Lord through a constant prayer. Prayer doesn’t have to be formal. It is all about connecting to our father at any moment of time.
Prayer is also crucial thing to avoid any sudden attack from the enemy. A Christian without connection to the father in prayer and through the Holy Spirit in us is like a fish thrown out of water waiting to die at any moment.
The other things that drives out the Holy Spirit in us and allows the sin of immorality to kick in is pride and over confidence. Pride always brings destruction. There is nothing we should be proud of except the Lord himself. If we are over confident and deprive ourselves what is the most important thing in life that is, constant prayer and interaction with the father, we might fall in to sexual sin.
Peter was too much over confident on himself that no matter what happens, he will never betray Jesus. In addition to that he was not able to pray in the time he needed it most. That is why he was not able to pass the temptation. But since Jesus had prayed for him so that his faith might not be tested by the devil, he was not eternally destroyed for his sins.