I think you need to give him a few weeks to cool down. If, and I suggest you let him b for a while, you have to talk to him, acknowledge that you agree that you both need space for the time being and leave it at that.
Because you have been on this stich already i dare to say you guys never resolved your problems, it is easy to go back to same ol' when the S is back. I want you to read "the proper care and feeding of Hs" and "love is tough" by J. Dobson which deals with separation.
Something wasn't going right, and I sure hope this separation is for the best of your M, something was festering between you two, he doesnt' want to go back for more of the same. Get a councelor and let him know you'll b going if he's interested, if he says no go anyways, you really need to talk to a trained MC, you'll benefit greatly, I promise.
Kids are too small now, dont' need to tell anything to the older one, just say that daddy is taking a break for now, that he needed some time alone, I got away with that one with my 8yr old when my H left for 8mths.
Cry but give yourself a time, arm yourself with good books and find yourself again, decide to claim the day for you each day and smile first things in the morn and than God for your health, for your kids, for other blessings.
Be not afraid...I will repay you for the years the locusts have eaten Joel2
30something 2kids survivor of S, MLC, A, D I have peace in my heart, at last.