My dear, I am not much on the practical side of things, I am more an emotional support type of gal.
Therefore my advice to you is to get outdoors as much as poss, with your son, across the parks and fields, to get that headspace. You don't need to be embroiled in his mess. Get out in the fresh air to let yourself think.
I can't believe you were just at work one morning, and randomly got called home, and walked into a complete timewarp change of entire life. It must have knocked you for six.
In some ways I think the conversation with her HB was coming. The chapter needed to be read, and now you have read it. It must be blowing your mind anew that he lied again, or got caught out lying again. It must be so huge to get your head round.
I read your early words, all the ones about coping, which you clearly have done, but as I say I am more worried now about the emotional fallout for you. You can get a counsellor's number from the yellow pages or google, you can have an appt made for tomorrow or the next day, if the shit hits the fan and you need to talk and grieve.
At the very least, I think that doing the minimum required to get through the days is the order of the day. No great projects unless you'd find them helpful. If you can't manage, don't. Bulk cook and freeze, early nights, get Bach's rescue remedy, allow yourself to cry, but as I say, the main advice I have is to get out into nature. Thats my best shot for you, dear stranger, to help you. Let the wind of change, forced as it may be, blow through your life.
XXXXX Thinking of you XXXXX