Tell Me About It: I slept with a guy I thought was single. Now I feel I’m keeping his dirty secret

PROBLEM: I am in need of advice. There is a guy in my group of friends whom I got with once last year. The next morning he informed me he was back with his girlfriend.

Obviously I felt horrible but I thought that they must only have been in talks about getting back together. This was last January.

Since then I have tried to avoid him and his girlfriend (whom he is still seeing) but have been polite and normal if I run into them in social situations.

A few weeks ago, on a group night out, his girlfriend left the house where we were drinking and he tried to get with me. I kept saying no, although he persisted for almost an hour. I kept saying, “No, stop, you have a girlfriend. What are you doing?”

Eventually I got him to leave. The next day I messaged him saying I felt horrible and he should really tell his girlfriend. He said he didn’t want to tell her as he didn’t want to ruin what they had as he really loves her. He begged me not to tell anyone and that “this wasn’t like him”. Then a week after that, he put a status on Facebook saying how it was his and his girlfriend’s first anniversary.

I put two and two together and realised that, when I had slept with him in January, they hadn’t just been in talks about getting back together but had in fact already at that stage been back together for a month.

Should I make him tell her, should I tell her, or should I say nothing? I feel like I’m keeping his dirty secret from his innocent girlfriend. If it were me I think that I would like to know.

I’m in a tough position, though, because he is in my group of friends. If I make him tell her it will ruin their relationship, and my friends will judge me and blame me for that. They think I shouldn’t say anything.

I’m confused about the best thing to do.

ADVICE: Firstly, well done on your stance. You have behaved very well during this whole experience. You fancied a guy and acted on it when you thought he was free, and, when it turned out that he was in a relationship, you refused his advances and asked him to come clean to his girlfriend.

The problem is with him, but it seems that you are the one who is suffering. You have told your friends in the group what is happening, and their advice is to say nothing, but I’m not sure if that will work.

If a lot of people in the group know about it, these things have a way of seeping out, particularly if there is a social event. This guy is not an honourable person, and there is no doubt that this will reveal itself in his relationship at some stage, but the possibility of you being implicated is very high.

It seems that there is very little chance of you emerging from this without someone getting upset or mad, but the person who is most upset at the moment is you.

You say that if you tell the girlfriend, you will ruin the relationship. This is not true. The relationship is already in trouble, and you did nothing to cause this – he did.

If you ask yourself what you would like to happen if you were in a similar situation to his girlfriend, you will figure out what you would like to happen, but there is no guarantee that this girl will see things the same way as you.

You have to make a judgment call. You will need a clear mind and to focus on all the facts. If you are caught up in worry or agitation you will struggle to make a decision, so perhaps you could give yourself some time to let your mind settle. Mindfulness might assist you in this.

You also need to be emotionally clear, and this is harder. You are no doubt angry and resentful at the position you have been put in. Try to accept that this has happened and remember that you are not the instigator of this problem.

Whether you speak to the couple or not, the group has been compromised and it is unlikely to remain the way it has been.

You have behaved well and are not responsible for the coming split.

Choose how to act from a calm and grounded place and do not add any extra suffering to the situation.

• Trish Murphy is a psychotherapist. Email tellmeaboutit@irishtimes.com for advice. We regret that personal correspondence cannot be entered into