Let Him GO. You do not need a man who isn't strong enough to handle this "mid" life crisis. For God's sake you have two YOUNG children, and he is going to up and leave! I would change the locks, and file for divorce, WHO the hell does he think he is? He needs space? WTF? and you don't? You are a good mom! and you need a man who will be there FOR YOU ALL in the long run, & HE ISN'T IT. I am sorry if I sound harsh, BUT it angers me that a man just walks out on his family. Because he can. This a sign by the way, he is seeing someone else. He will say isn't, BUT he is. Another reason to kick him to the curb. Please take care, and be strong, you don't need him, nor do your sons need to be brought up in that type of environment where the man can just walk away from his responsiblities. They deserve better than that!
I hope my rant helps. Stay Strong.
K.