Why do married people cheat?

Will you love her, comfort her, honour and protect her, and, forsaking all others, be faithful to her as long as you both shall live?” The groom answers “I will”. The minister then says to the bride: Will you love him, comfort him, honour and protect him, and, forsaking all others, be faithful to him as long as you both shall live?” The bride answers “I will”.
In my opinion, these are three reason whey married men cheat:
1. Ignorance

Some people don’t know themselves, how they are wired and what can easily tempt them hence they cannot avoid such situations and fall like a pack of cards. Some believe they are so spiritual that they cannot be tempted.
James 1:12-14
12Blessed is the man that endureth temptation: for when he is tried, he shall receive the crown of life, which the Lord hath promised to them that love him.  13Let no man say when he is tempted, I am tempted of God: for God cannot be tempted with evil, neither tempteth he any man:  14But every man is tempted, when he is drawn away of his own lust, and enticed. 
- King James Version
The truth is that everyone gets tempted. The fact that you’re married doesn’t mean you will not find someone else more beautiful or handsome than your spouse. You have to be prepared to deal with those situations when they occur and stick to your wedding vows.
Some are ignorant of the fact that marriage is ‘hard work’. You have to work at it, it is an investments! Just like a businessman would take care of his investments, you have to devote time, money and resources to spice up your marriage and keep the love alive. If not you’ll get bored and start to look for excitement outside marriage.
Some don’t know that men are from Mars and women from Venus. Totally different in the way they are wired. The man needs to study the woman and the woman likewise. Understand the different love languages, emotional variations especially ‘during the time of the month’, the man’s ego and need for respect.
1 Peter 3:7
Likewise, ye husbands, dwell with them according to knowledge, giving honour unto the wife, as unto the weaker vessel, and as being heirs together of the grace of life; that your prayers be not hindered.
- King James Version
The first 2 years in marriage is usually the teething period when the water is tested. Let’s see the real you, dating and courtship often are not reality, welcome to the real world. No two human beings are compatible even identical twins are not. The excuse that you are incompatible hence the need to go outside is fallacy. It is immaturity and the refusal to compromise in the relationship that makes people stick to the incompatibility theory.
Marriage requires give and take, love respect, effective communication and the guts to ride the storm when they come. If you think you just fall in love and get hitched and expect a bed of roses you are in for a big surprise and an early exit.
Marriage is sweet, but you must know how to live it right. Roses have thorns but don’t forget thorns have roses too.
2. Selfishness & Greed in Sex and with Money.

The man just wants to offload without realizing that the woman requires her need to be met as well, even if she takes time to get to there. Selfishness on the man’s part implies that the wife never gets satisfied and is left open to temptations so much that the nearest male seems a likely candidate. The same applies to the wife when she isn’t in the mood but the man is loaded and ready to fire. You leave him open to temptation.
A wise woman would probably marry a guy with potential and vision, a man that can take care of the family as a whole commitment to family life. This is not the same as marrying a man with just dream and sweet talk. The foolish woman would definitely run after the next sweet talker of rich guy when she discovers her man can’t take care of her.

 
3. Lack of self discipline

Some people cannot control themselves. The site of a nipple or anything in skirts sends thousands of volts to the brain and he loses common sense. Those people always say it’s the devil. Tell me how the devil unzipped your trousers and took off your clothes and that of the girl. Some girls also cannot live without spreading; even the brutal act of circumcision cannot save those ones.
Self discipline requires a conscious and determined effort to do what is right and doing it right even when no one is watching you. It is very important that one keeps him/her self chaste and pure for marriage. If while single you were moving from Peter to Paul or you were one of those guys saying Goodness and Mercy shall follow me, you’ll find it very difficult to stick to one woman for life.
Self discipline starts from your youth. No pre-marital sex, no fooling around keep yourself pure. Don’t accept the lie that you must test drive to guarantee that you are segxwally compatible before you get married. Again no two humans are segxwally compatible. You have to learn the skills, positions and techniques to get yourselves to cloud 9 every time you get it on in marriage.
If you invest in keeping your love life in your marriage hot, you will always be interested in your spouse whether she is size 6 or size 40, of whether he has peanuts or a pole. Size sometimes doesn’t matter at all the time. If you are so concerned there are ways and things you can research or buy to spice things up. True love, wisdom, honesty and faithfulness will always prevail.
There are faithful men and women in marriages, those that took their wedding vows and never looked back. A handful may be unhappy in their marriages but there are those that are happy and express the joy of their marriage. You may possess all right characteristics to remain faithful in marriage, the strength will and determination to remain faithful comes from within and the reverent fear of the almighty God.
2 Timothy 1:7
For God hath not given us the spirit of fear; but of power, and of love, and of a sound mind.
- King James Version
1 John 4:18
There is no fear in love; but perfect love casteth out fear: because fear hath torment. He that feareth is not made perfect in love.
- King James Version