Who does he expect to make his life better? You? Sorry, but that is not your job. If he wants to lay around the basement and sext to women, that's his decision, but bully for you for getting away from all that. You have absolutely no reason to feel guilty about having moved on with your life.
I agree with LTD that your conversations with him should be about the kids and related business only. Just flat out tell him that you won't discuss anything else, and then stick to that. I have had friends like that...always mopey and depressed. I eventually just stopped associating with them. Who needs all that negativity? Is there someone else who can watch the kids while you go to NAPA?