I met this guy through mutual friends from base. He is a marine, and I am in the usaf.
We've all been hanging out a lot the past few months, and I can tell there is a major spark between us. LOTS of sexual tension. However, he is married and just had a baby. He asked me if I'd be interested in hanging out when his wife wasn't home. I asked him how we can be so at ease with cheating. He said his wife has cheated on him many times, and they never have sex. He said average once every three-four months.
We are in the same class together at a local college.. so we got together to work on a paper due. It was very intense and he made it very clear he wanted to have sex.

I said no, and pretended I was super focused on the paper. However, I was Dying to do it. I can imagine how wrong it is... and that's why I haven't done it. But, I'm afraid next time I see him I won't be able to say no. PLEASE HELP ME. HONESTLY. JUST GIVE IN? OR KEEP FIGHTING HIM OFF?

If he's married the right thing is leave him alone.

FIGHT IT OFF. This guy wants his cake and to eat it as well. If he and his wife are having issues then they should work on that or divorce.

I suggest not hanging out with him anymore. Period. Nada. Zip. Zilch. I'm sure you can find another study buddy and certainly another romantic interest who isn't so taboo.

Speaking of taboos: they feel so much sexier than they actually are. After the initial thrill of "oooh we're doing something so bad" wears off-you'll be left with a lot of ick. A chemistry with someone who is unavailable is so often misguided.

And as far as any sob story he has about his marriage, I'd be willing to bet a lot of it is to get you in bed. Don't fall for it. Respect his marriage if he won't. You'll be glad you did! Good luck!

He's married. He may not give a damn about his wife, or his child, or the vows he took, but you don't have to give up your morals because you want a bit of slap and tickle.

There are other guys out there. Available guys. Guys that aren't cheating scum.

Don't lower yourself to his level. Fight him off. Tell him point blank that you don't have sex with married men, because unlike him, you aren't amoral.

Today you might be his toy... but tomorrow who will it be? Not you. If he cheats on his wife with you... if you ever became his wife he would cheat on you with someone else when things start to get dull. You WILL eventually find yourself on the other end of the same situation you are in now.

You don't 'keep' fighting him off. There should be one 'NO!' and nothing more on the subject. 'Keep' makes it sound like you are planning to allow more advances. Don't allow him to think you can be won over if he 'keeps' trying. If you have to interact with him, keep it class related. Be polite, but don't even try to be his friend.

Remember 'No!':
No discussion.
No 'if you weren't married... '.
No 'I want you, but... '
No trying to decide that some acts are not sex and others aren't.
No playing games.
No rationalizations about why wouldn't be cheating.
No accepting his excuses for why it would be okay.
No giving yourself permission to fantasize about him. It could lead to a weakening of your resolve.

As has been said, if he has marital problems, he needs to work on them with his wife. You need to stay out of it. Have more respect for yourself than to become the 'other woman'.

Something for you to think over: Men who cheat have a tendency to lie through their teeth about other things as well.

Take care of yourself. You deserve someone who is available to build a relationship with you instead of use you to prop up the relationship he already has.

Ask his wife if she minds sharing her husband. Are you crazy or something for even putting yourself in this situation. Plain crazy.