While you were driving home your mind was full of the joys of possibly having a special day with your now not so dear h, and you were completely unprepared for the scene that greeted your homecoming.
As a result your world has come crashing down around your ears, and it will take some considerable time to recover from the shock.
Until you know exactly what has been going on, and for how long and with whom, and with how many others, behind your back your imagination is going to run riot and you will suffer the tortures of the damned - unfortunately, this is par for the course, and the pain will merely shapeshift once the truth is revealed.
The fact that he has not yet had the grace to contact you suggests that he is either thoroughly ashamed of himself and can't face you, or he's desperately trying to cobble together some load of cod such as 'a colleague dropped by unexpectedly' or 'she needed support'.
Of course, the latter scenario is usually accompanied by an attempt to persuade you that he left and stayed away because he feared that you would be unreasonable, and the resultant debate would wake your ds etc.
You have behaved with considerable dignity, and you're best advised to batten down the hatches and only dispense information to others on a need to know basis otherwise you will find yourself dealing with the double whammy of those who get off on the misery of others and love gossiping, and your pride will be in shreds at the thought of numerous others knowing about the manner in which your h has humiliated you.
Embrace as much normality as you can with your ds over the next few days, and let events unfold. You can vent here where others will understand your pain and will be able to impart the wisdom they have gained from bitter experience, but don't underestimate the usefulness of an old cushion - stick his photo on it and kick the shit out of it, or pin the photo to a dartboard and enjoy taking precise aim - to relieve your feelings.
When you do eventually speak to your h, keep your breathing and your voice calm and put the onus on him to explain his colossal breach of trust before you reveal your feelings - and be aware that your feelings may undergo many changes before you know what you want to do in the longer term, and you're not obliged to rush to put him out of his misery.
It is sensible to secure your finances (clear out any joint bank accounts etc) so that you are at least in control of one thing in the middle of this madness, but resist the temptation to change locks and pack his stuff as that's the type of knee-jerk reaction that can make a bad situation worse - although slide bolts or on the front and back door are a necessary security measure if you are on your own, or with your ds, in the house.
Please know that you're not alone as many others are undergoing similar experiences right this minute, and please know that relationships can recover and can become stronger after being put to this particular test.
Above all, go easy on yourself and endeavour to regard this as a rite of passage which you will survive even if the marriage goes down the tubes.