DEAR DEIDRE: I AGREED to watch my girlfriend having sex with other men but it has ruined our relationship.

We were talking after making love one night and she described her sexual fantasy.

3 I agreed to watch girlfriend having a threesome with two men - but left the room after five minutes Credit: Getty - Contributor

She said if I agreed to do hers, she would let me do mine as well. She said she had always wanted to have sex with two other men while her partner watched. I was gobsmacked.

I didn’t want to rock the boat so I stupidly said yes. I am 29, she is 28 and we have been together for three years.

We have always had a good sex life and I thought it was satisfying enough for us both.

We did agree rules, though, such as using condoms and no kissing or cuddling these men afterwards. I wanted to be clear it was purely a sexual thing with no feelings involved.

3 My girlfriend said I’d ruined the night but did admit the men treated her like a piece of meat Credit: Getty - Contributor

She set it up and rather than have strangers, she brought in two male friends. While I was watching, they broke all the rules she had promised. She kissed and fondled them both and they refused to use condoms.

After five minutes I couldn’t stand any more and went out of the room. I heard her say she was going to talk to me.

I left the flat until the next day. My girlfriend was furious.

She said I’d ruined the night but did admit the men treated her like a piece of meat.

3 I have been sleeping on the sofa since the threesome as it makes me feel sick Credit: Getty - Contributor

It makes me feel sick every time I think about it and I have been sleeping on the sofa since.

She has now told me she stopped taking the Pill at the time, as the chance of getting pregnant by one of them made it more exciting. I don’t know if she was lying or not.

I can’t talk to my family about it but I have talked to one trusted female friend.

She said I should leave my girlfriend and called her a tramp. My girlfriend says that this friend is trying to split us up because she wants to be with me herself.

She says if I leave her, I’ll never get anyone as good as her.

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DEIDRE SAYS: Setting up that threesome wasn’t so much cheap behaviour as self-destructive.

Your girlfriend must get an urgent sexual-health and pregnancy check.

I wonder what lies behind this fantasy of hers.

Did your girlfriend not realise she would end up feeling used in this kind of scenario?

Ask what has led her to feel drawn to such risky sexual behaviour.

There has to be some basis for it and understanding that might help you move forward together.

My e-leaflet on Sexual Fantasies could help you talk this over.

But if you know deep down you will never feel the same about her again, splitting up will be best for you both.

In that case, take time to get over the split before getting involved with anyone else, whether that is your good friend or not. You need to give your hurt a chance to heal.

Get in touch with Deidre today Got a problem? Send an email to problems@deardeidre.org. Every problem gets a personal reply, usually within 24 hours weekdays. You can also send a private message on the DearDeidreOfficial Facebook page. Follow me on Twitter @deardeidre.