This is quite raw for me, but here goes. I have known my wife for 15 years. We have been together for 10 and married for five. We have two children – my stepson is eleven and our daughter is seven. We have had our difficulties over the years, mostly due to intense stress in both our work lives and with our parents. My parents both died relatively recently. My wife's parents have always had a really really bad relationship with lots of control, shouting, absence and possibly cheating.

My wife started to act oddly earlier this year. The phone was locked and never out of her grasp. She started to go away for long five- or six-day weekends – totally out of character. Both I and the kids were really upset. I have recently discovered she is seeing someone. I pretty much know everything including a shared diary detailing when they are away.

My wife flatly denies everything. According to her she is with work friends. That's what she tells the kids as well. She has told me we should separate – but then she says we shouldn't. Her latest is that we stay together in the house for the next x number of years. Says we are not a couple at the moment, but she doesn't know what the future will bring. We are even going on a two-week holiday in the summer as a family, a holiday I was originally told I couldn't come on. It's like she is living two totally separate lives.

She recently told me she doesn't want to live with anyone else, doesn't want to create a new family, and doesn't do casual sex (in a response) to a fairly upset question from me. She has a history of going off the rails somewhat, but never admits to that. She has said there needs to be more to life than just the kids and work, and just wants to feel good about herself. I feel deceived, devastated and just don't know what to do. I need to be strong because of the kids but its killing me. I don't see how she can realistically run two lives – but in her head she appears to be doing it. It's almost as though they a parallel and never meet. It's only when it gets close to her going away and the two lives start to get a bit closer that there is friction.

I know quite a lot about the man she is seeing. He is a single dad with two kids. I cant see how he can be happy if hes interested in her with this arrangement – sees her maybe every three weeks, still lives with her husband. I just don't know what to do. Divorce her, hold fast and see what happens or what? It's just killing me.