Have you ever been "the other"?

Are you sure they are cheating? Perhaps the engaged couple has an open relationship or some other kind of arrangement. Only if you are sure that nothing like this is happening is there a moral question to be answered. If there is cheating going on, though, then it is worth raising the question. The other “other,” which is to say the person unknowingly marrying a cheater, deserves to know what s/he is getting into; and the person in the middle has no business getting married if s/he cannot be honest with however many partners s/he has.

Often the person being cheated upon looks upon you as the bad guy if you intervene. I think most people know, at least on some level, what the other is up to. They just choose to ignore the signs or repress the suspicion. I also think that if the relationship were healthy, no one would be cheating in the first place. With regard to the morality, I don’t believe the job of enforcing or judging morality is up to anyone except the individual. That said of the person being cheated upon were my best friend, I would probably have the chat and hope for the best.

I wouldn’t intervene at all. If you are happy to still be friends with this person then I would leave well alone as, in my experience, these sort of situations are never exactly as they seem! I find it very strange that the person your friend is seeing is still planning on getting married as, I agree with @rooeytoo that, if the relationship was healthy/happy no one would be cheating. If you’re not happy with who you are engaged to, now is the time to get out of the relationship because it’s much harder to do so after the wedding! I fear your friend is in for a lot of heartache and, if you are able to put the moral question aside, you may need to be there for them when/if things go wrong.

I would raise moral questions and have when my best friend was going with married man. You need to be true to yourself.

If it was me, I would think about letting the engaged innocent party know too.

It would effect the friendship for me, as I would not agree with the duplicity and what I consider lack of integrity. I would let the friendship go.
Otherwise I would be a hypocrite, professing to not agree with duplicititious behaviors but looking away from it at the same time.
Nope, wouldn’t work for me at all.

Whats the point of marrying if you still want someone on the side and you are not in an open relationship?
I see the situation as illicit, dishonest and immature, qualities I do not want in my relationships.
Uh uh…I do not agree with being party to the duping of another innocent person.

@rooeytoo is right about the ability to live in denial. I have seen it and it looks really strange, but the desire to hold on to the marriage seems to outweigh the need to see or admit the truth, or deal with the truth.

If you know the other parties involved, there is going to come a day when you may have to be in a room with the three of them. Do you really want to keep that relationship and put yourself in that position? Do you want your friend to call and ask you to be an alibi to their trists? That could happen as well.

Distance yourself from it if it bothers you. If your friend asks why you don’t hang out anymore, tell him/her you are actively avoiding his/her love life because the idea is awkward for you.

I have no room in my life for liars. If they are easily willing to do this to another person than you know they can easily betray you in the future.
I would let them know that I believe they are behaving in a horrible manner. They are willing to let someone walk down the aisle believing in a lie. I would also let them know that the person they are cheating with is also a liar and is only using them. Proof is, if they weren’t then they would dump the other person and move on with them. She or he is not considering that this will eventually blow up and there may be children involved in the future. So it won’t be just adults ruining other adult lives. They will probably be the cause of ruining some child’s future. There are plenty of single people if all they want is sex with no string attached.

I think it is appropriate to raise questions with your friend and to urge them to take actions you think are right. However it is inappropriate to raise questions with anyone else, unless you know them as well as you know your friend.

You may think you know what is going on, but it is highly doubtful that you know much of the story. The details, if you knew them, might change your opinions quite drastically. I would hesitate to assume I knew anything just because I knew the very broad outlines of the story. The devil is in the details, and I doubt very much you have many of the relevant details, no matter how much you might think you do.

I say that because in my experience, most people act like they know a lot more than they do about personal situations. They hear a few lines of a story, and automatically fill in all the rest without even being aware of all the assumptions they are making. I think it is always wise to caution yourself that you don’t know nearly as much as you think you do.

First of all thanks everyone for all your help I guess after all everyone did had a certain reason in each answer!

Second, I just wanted to let you guys know that I talked to her and her short response took every words of my mouth…

She claims that there’s not nothing imoral about being the other as long as you do it for love and she accepts no responsability for her actions defending that if there’s a problem is only between the couple.

Third I don’t know what to do now: part of me doesn’t want her as friend anymore, because clearly it’s not someone one can fully trust, but other part of me feels too judgemental and maybe a little too rough on the situation and taking in consideration that we’re on the XXI century… I feel I might also not being such a good friend for “not understanding” that people do pretty much every crazy things for love…

What do you think about her position and what would you do in my position?

There’s an old joke where a lawyer tries to argue with a judge. “Your honor,” says the lawyer, “my client was out of town on the day of the murder. And if he wasn’t, he was not at the scene of the crime. And if he was, he didn’t pull the trigger. And if he did, he’s insane.” Your friend also sounds like she’s trying to have things both ways: there’s nothing wrong with her actions, she says, and she’s not responsible for what she’s done even if it was wrong. Your friend may not be guilty of adultery (depending on how we wish to define that term), but she’s certainly guilty of aiding and abetting.

As people living in the 21st century, it is perhaps incumbent upon us to recognize that monogamy is not for everyone. It is not incumbent upon us, however, to condone cheating. There’s nothing wrong with having multiple partners so long as everything is consensual. But if one person has explicit reason to believe that they are in a monogamous relationship while the other has sex with other partners in secret, then the latter is exposing the former to risks to which s/he did not consent. Non-monogamy is one thing; cheating is another.

Do people do crazy things for love? Absolutely. But that is an explanation for her actions, not an excuse for them. She deserves your sympathy, but not your approval. It would be one thing if her “crazy actions” were merely out of the ordinary or extreme. The problem, though, is that they are not merely those things. Her actions are dishonest and inappropriate. If I were you, then, I would not give up my position in the name of friendship. A friend is someone who tells you the difficult things that you need to hear. I would be clear that I cannot make the decision for her, but that I had strong opinions regarding what the correct and incorrect actions were in this situation.