Oh Lesson, enduring my own nightmare at the moment and reading your post just tipped me over the edge and the tears are rolling.
I think it would be safe to say that I was in your wife's shoes so whilst my opinion might not be easy to read its given with best intentions and to try and help you in the situation you find yourself.
You certainly need to tell you wife, preferably face to face via a mediator/counsellor if necessary but she needs to know how you feel and why you feel that way in order for her to have acceptance and closure if that is indeed they way matters head.
Most mediators and counsellors would say the vast majority of their clients seek help "too late." However I believe you owe it to your wife and children to at least try and enter into
mediation/counselling which not only helps keep relationships together but can also be very helpful in negotiating the ending of relationships.
Unlike my ex you don't sound uncaring towards your wife albeit that right now you know deep inside you don't love her the way you perhaps used to and the fact you say "if ever" hints that there is something within this relationship that has never quite sat right with you.
Divorce and separation doesn't necessarily mean pain and suffering I do realise that but my own experience is that it is unbearable in its pain and suffering and no matter how hard you try to make life "normal" for the children it will never ben "normal" if you and your wife part. The "normal" will become "different" and the difference invariably means pain emotionally and physically as one home splits into two and the cost of maintaining two homes becomes an issue.
Little things you may possibly take for granted right now will become huge whopping issues unless you deal with it now. It won't be easy and your wife will, if like me she has no idea of how you really feel, will be devastated and most probably very very angry and upset.
Please seek out counselling/mediation now, remain honest and focused and I truly pray you find the solution that is in the best interests of all your family be it divorce or indeed a new beginning of a life already in place.
God bless
Jeannie