I agree with Raspberrytorte. Also, if your husband says ONE THING about your 'moods' tell him being upset is normal, and his ability to just be fine is a sign that he wasn't as emotionally invested in the family. No wonder he might be cheating, he has no heart in the house. Just going through the motions.

Now that the funeral is behind you, no need to hide anything from anyone. He can tell his grandmother in his own time. That side of the family is his responsibility. You can maintain any relationship with anyone that you want to, if they feel comfortable to reciprocate. What is most important isn't protecting relatives feelings from the truth, but taking care of yourself.

Try to continue care of your physical health, and your surroundings. You don't need him sneaking around taking pictures of messes to try to confirm some outlandish tale about you.

Keep reaching out. Don't suck into yourself. Your insides are not dying - everything that you thought your life was seems to have ended. That feels physical for you because your identity is being ripped apart. You won't die, and you will regrow a new reflection of life. But this breakdown is very normal -this is why people explain how horrendous divorce is. No med in the world can make it go away, but continuing to care for our mental health can reduce its getting out of control.

Live in the moment you are in. Think about the future only as far as you are required to. Not big day dreams, but real plans for appointments, paperwork - etc.

Try not to indulge in self pity and wallowing for too long of periods of time. Give yourself an amount of time, but try to impose restrictions upon yourself. 15 minutes, an hour, after 7pm - then get up, get back, and push through, if not for yourself then for your children. Tap into anger if you need strength and it seems to come from no where. Anger can be a great lever for energy when we feel that all is lost.

Consider cut, copy, paste with this Poem: Desiderata. I have found it can give me strength and insight and have kept a copy of it in my kitchen since I stole the plaque from my moms house when I moved out at 18. Yes, I admitted it too her decades ago.
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Desiderata

Go placidly amid the noise and haste,
and remember what peace there may be in silence.
As far as possible without surrender
be on good terms with all persons.
Speak your truth quietly and clearly;
and listen to others,
even the dull and the ignorant;
they too have their story.

Avoid loud and aggressive persons,
they are vexations to the spirit.
If you compare yourself with others,
you may become vain and bitter;
for always there will be greater and lesser persons than yourself.
Enjoy your achievements as well as your plans.

Keep interested in your own career, however humble;
it is a real possession in the changing fortunes of time.
Exercise caution in your business affairs;
for the world is full of trickery.
But let this not blind you to what virtue there is;
many persons strive for high ideals;
and everywhere life is full of heroism.

Be yourself.
Especially, do not feign affection.
Neither be cynical about love;
for in the face of all aridity and disenchantment
it is as perennial as the grass.

Take kindly the counsel of the years,
gracefully surrendering the things of youth.
Nurture strength of spirit to shield you in sudden misfortune.
But do not distress yourself with dark imaginings.
Many fears are born of fatigue and loneliness.
Beyond a wholesome discipline,
be gentle with yourself.

You are a child of the universe,
no less than the trees and the stars;
you have a right to be here.
And whether or not it is clear to you,
no doubt the universe is unfolding as it should.

Therefore be at peace with God,
whatever you conceive Him to be,
and whatever your labors and aspirations,
in the noisy confusion of life keep peace with your soul.

With all its sham, drudgery, and broken dreams,
it is still a beautiful world.
Be cheerful.
Strive to be happy.

Max Ehrmann, Desiderata, Copyright 1952.