Unreasonable behaviour?

My wife completely out of the blue after 17 years of marriage decided to end it. Obviously in this situation we'd have to wait 2 years to get divorced.

I have now found out since August last year she has been meeting another man, who told her he likes him in, secret even in our home while I was at work. They haven't admitted having sex but I know they have been in our bedroom on 2 occasions.

Would this constitute "unreasonable behaviour" for divorce?

>>Obviously in this situation we'd have to wait 2 years to get divorced.

That is not true and most people would be very unwise to wait for two years if the marriage has broken down irretrievably in the here and now.

When a marriage breaks down beyond repair almost everyone can rely upon unreasonable behaviour. I would be surprised if your case was any different. You may need help in putting what is required or you may need to do some more research on unreasonable behaviour.