Recently, my brother-in-law accidentally forwarded me a text which led me to find out that he's signed up for an internet dating site. He and my sister have only been married eighteen months and have a young baby, so I'm completely shocked that he could do this. I'm scared that my sister will shoot the messenger if I do tell, but I know it will devastate her if she finds out later that I knew and kept quiet. Help!

Susan advises

This is what you do. You approach not your sister, but your brother-in-law. You tell him that you know the situation. You tell him that he must spill the beans to your sister. You give him a time limit on this, and warn him that if he lets that time limit go past, then you will spill the beans for him.

You also tell him that you want his marriage to your sister to work and that you will be there for both of them, cheering them on, as they try to work things through. With luck, this man will face the music - and he and your sister will then go to counselling, get help and get past this crisis.

If he doesn't, then even if your sister does shoot the messenger, once she has recovered from the shock and the pain, she will realise that you were in an impossible situation and that you acted in the best way you possibly could.