WTF?! Wow, if you really have to ask this question, there is either something seriously wrong wit your morals or you need mental help. Cheating tells a lot about your character (and yes, you'd be cheating too, even though you aren't in relationship).

A moral obligation....are you kidding me? Wow, is being a decent person with some integrity, compassion and caring for others (golden rule) that big of a mystery to you?

I agree with the person above. You need some mental help.

Please tell me this question is some kind of joke. Please...

What if you were the girlfriend? Can you, even for a minute, put yourself there? Doesn’t look so fun from that angle does it? Life would not be so cloudy if you look at life through the eyes of others. If that doesn’t help you decide what to do, remember that Karma will be a far bigger bitch, than the GF, when she finds out.

This is something I've been conflicted about recently. Not because I would ever consider cheating, or being the other woman. My best friend of a decade recently slept with a guy that we're both friends with, who has a live-in girlfriend. She rationalised it by thinking "She's not my girlfriend, it's not my responsibility to make sure she doesn't get hurt." I was shocked at the time that she told me, and did not voice my opinion. But to be honest, I doubt I can ever trust her again. She's very good friends with his girlfriend, and if she can do that to her, I'm keeping her the hell away from my boyfriend.

Keep it in your pants, you don't have the right to destroy someone else's relationship.

This is exactly like ScarJo's maddening character in He's Just Not That Into You!! Honestly, the things women use to justify their role in infidelity. No, it is never okay. And yes, you are a terrible person. I'm not afraid to judge especially when the asker shows so little remorse or empathy towards the wife. He's spoken for. Back off. There's plenty of other fish in the sea, so why go for the one that's already been hooked?

Wow. I am sorry but that is sad. Whoever asked needs to get checked mentally. Being the other person, feels awkward not to mention wrong.

If the boyfriend is flirting, back off. Have respect for yourself. If he's flirting with you, that means he'll flirt with other girls once he gets bored with you. Save the drama and keep your legs closed. If you have any morals left, you'll let the girl know. (If she hasn't figured it out already.)

It's not that he's interested in you. He's interested in anything with boobs and a gullible enough mind to fall for him.

But hey, if you don't mind that he'll cheat on you once he has you, go for it. After all, how can morals and friendships to compete with this guy you met and hit it off with?

If you go ahead with this, you are playing an integral role in hurting another person. No excuses. Is it okay to aid a murderer if the victim was just going to die anyway?
That said, I think that everyone's being a bit harsh on you. Not because they're wrong, but because it isn't their place to judge. I've had friends who have done bad things, but aren't necessarily bad people- we all screw up from time to time, become blinded by temptation or emotion. What my friend does is between her and whomever else it affects. No person is superior to another- you are not answerable to your friends, and you don't owe them any excuses. If they're really your friends, their compassion for you will not be conditional on their moral agreement with your behaviour, especially if it's none of their business.
Do the right thing because it's the right thing, not because you're afraid of other people's poor opinions.

I feel like it is definitely wrong! I mean you can't help who you're attracted to, I understand this. But I mean come on! You are destroying the relationship of another person. It's like walking up to the poor woman that is probably head over heels for this guy, just hauling back and smacking her in the face. Not just you...both of you guys. It's emotionally damaging! I can idnentify with being the decieved lady. I've had this happen to me and it tore my world apart. Hell! That was my first ride in a police car. The "other woman" actually came to my door and asked if I'd leave my own house because she was going to move in with my boyfriend. Poor Hussy never realized that we did not live together. I guess all those nights at her place he failed to mention he lived with his mom. I lost all control and attacked her. I know it was wrong. But how do you think you'd feel if that happened to you? How would you like to feel abandoned, worthless, insecure and ugly? That's how you'll feel when people start giving you looks and talking about what you did to her. I bet you're a better woman than this. Just don't do it. It's wrong. And it'll only get you cheated on in turn too. You can do better. And apparently so can his girlfriend.