NAP, you chose a good name! I feel you're right not to be "Pollyanna-ish" - largely because I don't think you can fix life problems by pretending they're not there. It's interesting that you experienced money problems, bereavements and suchlike during the years your children were small. Yes, "that's life" but these things knock you around some.
I don't know what age you are, but a swift estimate would put you at around 40. There's a reason why the 'mid-life crisis' exists. It's the point where we start to evaluate the first half of our lives, review how well we feel we've matched up to our own expectations, and begin to make revisions & plans for the second half. It is also the age at which "real life" comes home to roost. People we love start to die - and, however well prepared you were, the first close bereavement is a bastard. Money problems become more threatening, in the light of our life review situation, and we feel a greater sense of urgency around any ambitions we still hold, but have yet to fulfil. It's quite heavy going for most people.
So, yes, "that's life" as you say, but you'd have to be a spectacularly shallow individual to sail untouched through all these life events!
As you're not shallow, you feel all the effects despite trying to dismiss them. With all this - very interesting, but emotionally challenging - stuff going on, you've also raised 3 kids: one of the greatest challenges known to mankind! I bet you're tired
Other people have offered good advice on the coping with parenting front. I'd like to add that it's extremely important for you & DP - separately and together to take plenty of time out. Discuss the big stuff, along with the small stuff. Get away for romantic weekends. Make some new plans. This business does matter, for it will determine how you navigate the next 20 years or more. You both deserve more attention - in yourselves, and from each other - so start prioritising.