The comments that he has made about growing distance and apart are script and are usually heard when their is op in the picture or waiting in the wings. He's moving forward in his head and he thinks that a divorce will help him get to where he thinks he wants to be. Again, script. If you were to ask him about these comments, he very well may not have answers or they will be the answers of the day, like the flavor of the day. Then again, the answers he provides to you may not be what you want to hear at this time. Best not to question too much what he's been scripting.
Of course he doesn't feel comfortable or engaged at home and w/you and the family. It's because he's changing and the depression is eating at him. He most likely felt closed in or was suffocating from what he perceived as responsibilities, etc. These are his feelings, just as you have feelings about the situation and right now, he'll shut down if you were to address how you feel. Keep in mind, this is all about him and what he's feeling/experiencing. He truly can't feel anything for you because he is too emotionally spent on himself.
He's not ready to hear the word therapy. He doesn't see anything wrong w/the children and in his mind, they'll recover and bounce back in no time. You will have to be the one to take them for therapy. Don't rely on him to be a responsible adult and work w/you on this.
Again, you can say all the things you've mentioned about how YOU feel and it will go in one ear and out the other because he's focused on himself right now. It's the "me, me, me" song and dance. The only person he can focus on and be selfish about is himself.
Write letters to him expressing yourself, but don't give them to him. It's better to vent here because what you may say to him about your feelings, etc., may push him away a bit further and he will shut down on you. There will come a time when you will have the opportunity to say what is on your mind, but now isn't the time.
Keep the focus on you and what you need to do to move forward. Keep the focus on your children for they need you, their mother and adult, to be there for them.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.