... if you write about it (to us or to a diary), it might help. It might not be cathartic, but it might help. Catharsis can come in little bits and pieces if it is a stream, steady or otherwise.
Aside from treatments (medication, talk therapy), I don't know how that internal dialogue goes for you, but give this a try.
Stop fighting it. Not giving in, but going around.
Easy for me to say, difficult for anyone in your situation to do. What I suggest is that when life really gets you down, and something inside tells you something negative, say to yourself "Oh, you again. Yeah, life is tough." And then take you focus back to what you are doing. If you aren't doing something and aren't distracting yourself with something like video or games, etc., try writing.
Try writing about your feelings, not to wallow in them, but to acknowledge them and to really really enforce the idea that they are only feelings, however sincerely felt, and I do not doubt they are sincerely felt.
I think your sense of duty is a good anchor for you. Your duty to your wife is not only commendable, but healthy. You may feel duties to other causes. Don't let them rule you, but they can steady you. They are something you can focus on, not because you have to, but because you have chosen to.
As to anxiety, meditation is helpful, as has been measured by studies. You can even do meditation in daily activities. As you are cleaning up something, focus on the task. "Okay, got that bit, here's another, needs scrubbing, where's the scrubber, okay, gonna hafta rub hard, harder, got it, where's the water, ....". In classical meditation, people are often suggested to focus on their breath. Feel it come in, feel it held briefly, feel it exhaled, feel the brief pause, repeat cycles.
You can take a 30 second pause at times, and simply focus on five breath cycles, nothing else. A grounding pause.
When negatives or depressed thoughts come up as you are doing something, acknowledge them briefly, and then move your focus back. The thing is that if you try to fight negative thoughts, it makes them stronger. Go around them.
It doesn't hurt to from time to time remind yourself of your goodness and the goodness in the world. You are a good partner. The world still has much tremendous beauty. There are many good people helping others and themselves and nature. It is a truth, not glibness. Don't so much focus on the goodness, but keep it in your back pocket. Use it not to fight the bad wolf, but to balance yourself from time to time. "Yeah, it's bad now, but there is good, so I carry on."
It does get better. Accumulated age accumulates experience which generates bits of wisdom which help balance.
Feed the good wolf. Starve the bad one without pretending it is not there.
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