Originally Posted by Tiberius

Sorry, but I find he other two replys very harsh and unhelpful.

Unless you sit down and air all your grievances with your wife, do not make any assumptions and plans.
You have been together a long time, have 3 children and if she means anything to you you need to get to the core of the problem. I do not think DNA testing your children will help. You have raised those kids as yours( and most likely they are) and what good would it come out if you find out that maybe one is not yours? What about your child?
Talk to her, she might be talking about treesomes and sending explicit emails because she does not get enough sex in her marriage. You need to come to the bottom of it before you split the family.
As for the messy house, I have a friend who works, her husband works less hours and he does most of the housework. I would call not call her lazy, she just has different standard of cleanliness from me and after 8 hours in the office, who wants to cook dinner and clean up afterwards?
If you can afford it, get a cleaner and cook simple food that takes very little effort to prepare. Like this you can be on the couch with her asking her how her day was and giving her a cuddle.
And your kids are old enough to do chores. Get them to chop the vegetables, reward them with pocket money when they wash the dishes, clean their rooms, vacuum the lounge.... If all muck in, life for you would be easier.
Talk and spend time together, divorce is the last thing, the very last road after everything else has failed.
And lastly, do check why she is staying late at work as my husband was doing the same and he had an EA with a co-worker.
You seem like a nice guy, stay that way and work on your marriage.