Here's the thing, if you or the marriage were so bad, he wouldn't have stayed as long as he did. The two of you created a daughter today and shared many good memories together.
You are in the early stages of his crisis and you are trying to find answers, but the answers aren't for you to discover. He needs to find the answers to his unhappiness and accept that he can't go back in time and change the way his life played out at the time he was emotionally stunted. He can visit that time, face those demons, accept that he wasn't at fault for the way he was treated and begin to grow up. None of this is on you. It is all on him and the authority figure (mom, dad or someone else).
How do you get thru the bad times? Feel the pain, allow it to wash over you and then release it. Find things to keep your mind busy. I did hundreds of jigsaw puzzles in the beginning, as well as becoming a workaholic. When I began to settle down, I started walking and doing fun things again. I came to this forum a month after my xh walked the second time in 7 months and have been here ever since. Why? Because I want to learn as much as I can about MLC, depression, etc. When I first came here, I read every book, met with people who were in crisis or finished up their crisis and visited w/people in shelters to better understand abuse. That's how I got through the tough times.
Amy, you have to decide how you want to deal w/your tough times. Use your time wisely, but have some fun in the process. Just because he's out to lunch, doesn't mean you have to be too. Once you are feeling better, you'll be able to do some things such as take up a hobby, join a social group, etc.
I promise you, it will get better....
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.