Why would a guy who is in a serious, long-term relationship (considering marriage with gf) flirt and want to have sex with another woman? He states that all is "great" with his girlfriend, yet he is contantly flirting and recently had sex with another girl... Don't get it! And he is thinking about marrying his girlfriend!!

How do you know he cheated?

Cheaters cheat, because that's what they want to do, and what does that have to do with relationships, or marriage? They are also liars to hide what they do, so they can keep doing it.

They are also selfish, and its all about them, and what they want when they want, and so make lousy partners whether dating, or married.

Don't question why, just make sure they don't do it to you, by leaving them alone. That simple.

Your thread is my boyfriend cheated so I assume it is something that has happened to you.
We still need more details though.

Your thread is my boyfriend cheated so I assume it is something that has happened to you.
We still need more details though.

The title was a typo... I was doing a search, and mistakingly left that as my title. This is something that happened to a close friend... and I'm angry for my friend!

Ok,he's a jerk. Some people cheat and they lie, so I hope your friend dumped him.

Cheating happens. That's why we emphasize that a couple should really get to know one another first before they truly commit to marriage.

You can't control the actions of a cheater. But it's better to find out the truth than to be left in the dark.

Your friend needs to decide whether she can still trust him anymore. Though, I don't see how she can anymore.

Again how do you know this person cheated. Is this a close friend because you are the one that cheated with this person? Or what? How do you know?