What will make a guy cheat on his girlfriend?

A complete lack of morals, integrity and character.

Not feeling appreciated by a nagging princess, crazy psycho.
Don't ever say I sugar coat things, now...it's true.

It can be any of the following reasons:

1. He doesn't care much for the relationship with his girlfriend so that he is willing to take a risk;
2. He feels a void in the relationship that another person can fill;
3. He doesn't find the relationship exciting anymore;
4. He met another girl whom he finds more interesting;
5. He has the opportunity to cheat; or
6. He needs to feed his ego.

And the list can go on and on ....

this is not the correct question. the correct question is "what will make him NOT cheat?" some guys are ******** and will cheat regardless and some guys are just so beaten down that they WON'T cheat no matter how ruthless or horrible said girlfriend is. however the majority of men, or even just people are somewhere in the middle-- they can be driven to cheat by an unhappy relationship. therefore, keeping the relationship satisfying is what one needs to do. note, however that if the relationship has gone so sour that cheating becomes regular it may NOT be salvageable.

He is a womanizing piece of dirt with a weak ego; with an overwhelming need to prove his manhood through sexual prowess.

A gf like twix5000

It's the easier thing to do.
Homo Sapiens struggles with monogamy because it is not natural.

Usually for the same reasons a girlfriend will cheat on her boyfriend. Pay attention to the confessions and stories here on EP?

Not talking to his girlfriend about whatever the problem is in their relationship. Too many women punish their men for being honest, so they are afraid to talk out the difficult things. This doesn't justify cheating, though. A real man will face the difficult issues and fix them, or end the relationship before he goes looking for something else.

well, him being a guy, and guys being selfish, self centered, sex obsessed, ********...

He couldn't get along well with his gf; sex, habbits, etc
He found better girl than his gf
His gf doesn't trust him
He is a playboy
He is Gay ! Lol ...

because he is selfish

His priorities...maybe having freedom/fun and experimenting is more important to him that the safety of a loyal relationship

All men are totally self absorbed its all about their dicks and ego

Because he doesn't really love her.

Not respecting the one he's with, or the one he's with not respecting him. If he's not getting at home as well, he will go somewhere, as bad as things are, men NEED sex, it's their stress relief, not just their pleasure.

Cheating happens when the love fuel tank is empty at home. If both parties are keeping the tank full at home, then the idea of cheating will be foreign to him. If he's a moral person and not getting the type of love at home that he is craving, then he'll look for other avenues before cheating. Look at the 7 love languages to see which you are and which your partner is and try to give them what they need. They won't go if you make the effort. My wife made me read the book.

being weak...........

getting bored with their relationships. not getting enough..loosing insteresting and finding someone better. the guy friend's influence and the list go on