my fiance who been with for nearly 6 years has just told me she kissed someone last week i dont know what to do i know it was only a kiss but i cant get my head around it and really struggling help?

It will be a struggle to process this because of the expected trust from your partner... but it's good to identify the reasons behind it. It's easy to assume the worst case or more so react very aggressively (whereas retaliation is fine) but if you get to know more about the situation, then you can make a much better solution for it

Did she say why she did it? She could be worried you guys won’t last longer. Maybe she feels like you loss interests in her. Or maybe she is unsure about your relationship. You guys need to sit down just the two of you and talk about what’s going on between you. Remember communication and honesty is the most important thing in a relationship. She told you about the kiss which is a sign that she feels guilty and wrong. Just meme we just because you feel like your relationship is perfect that doesn’t mean it is. Her actions may even be a serious cry for help

Yes, it’s only a kiss, but I can really understand how you are struggling with what she did. Talk to her. Since she is your fiancé, it’s important for both of you to take a look at your relationship. Be honest with each other. If there are trust issues now, it will only get worse if you don’t address what is going on with your relationship. Once you are married, a betrayal of trust with an unfaithful partner may be much more painful. Maybe she is seeking more attention. I hope you find the answers you need by having a serious discussion with her.