I know it’s wrong and yet I can’t stop. 

I’m 44 and my wife is 36. My mother-in-law is 57.

When I first met my wife, 15 years ago, I remarked to a friend that I’d lucked out. 

They say if you want to know what your partner will look like when she gets older, look at her mother – and hers was a stunner. 

But I was madly in love – and lust – with my wife then.

I’d see my mother-in-law at family gatherings. I made her laugh.

But my wife didn’t get on with her well.

Fast forward 15 years, and my wife and I now have two teenage children and have fallen out of love. 

We rarely have sex and we bicker all the time.

Last month, my mother-in-law, who is now widowed, came to stay. 

I work from home, so we chatted a lot.

When my wife went to bed early, we had a few drinks together. She said she’d noticed we didn’t seem as happy, and asked if she could help.

I opened up and, to my surprise, she said she’d always thought I was too good for my wife. She said if I were her husband, she’d treat me a lot better. 

Somehow a hug turned into a kiss, which turned into a passionate fumble on the sofa. 

We pulled away but, the next night, it happened again and this time we had full sex on the living room floor.

It was such a terrible thing to do, it made it even more thrilling.

Since then, we’ve been having sex every day while my wife is out at work, and the kids are at school.

She’s going home soon, and although I feel guilty, I don’t want to stop this affair. 

DEIDRE SAYS: If you’re looking for permission to carry on, you won’t find it here.

This isn’t just cheating on your wife, it’s a double betrayal.

They may not get on, but your mother-in-law is still her mother. If she finds out, she will be more than devastated.

It will tear the family apart.

You must put a stop to this. If you’re unhappily married then talk to your wife and either work on your marriage, or decide to split.

My support pack, Looking After Your Relationship, should help.