Bonsoir - I agree with you and disagree with Anniegetyourgun.
What you need mothersmilk is for you and DH to sit adown and talk about your hopes, your dreams and what you want in life. Dont inhibit yourself by thinking you cant do something. Get some wine and nice food in, get the DCs shipped off to grandparents. Talk all night until the dawn breaks if necessary. Couples don't do this enough in my view.
You are that dreaded '7 year itch stage'. You have had your DCs, you are married. The excitement wore off and the bills still need paying and DH is thinking: 'is that it then, the same thing for the rest of my life?'
It is not disatisfaction with you, it is disatsfaction with life in general. It is NOT enough for him, that is all he is saying.
I have said it before on other threads so apologise to those that have read me say this before but me and DW constantly try and renew our life together. We do it every 7 years or thereabouts. Change is part of our life plan. We are emigrating to New Zealand next year. We want to go while our DSs are still young enough. They are 8 and 10 now. We know we should have gone 2 years ago but illness intervened. Now we are defintley going, barring unforseen accidents.
I do not for one minute believe your DH is seeing someone else (or even thinking it) but I often wonder if sometimes that happens when people feel life is passing them by.
Dont just settle for you 'being Mum' and him being the 'dependable hubby' routine. Take a risk, live life, dont just wait for death.