Thank you for requesting my help.
It is very difficult on you when he will not accept responsibility for his own behavior. Until he does, there is going to be little you can do to change him. The only thing you can control is you.
You can try talking to him again about taking responsibility. Given that you are on the verge of leaving the marriage, try telling him you are willing to give the marriage a last chance, but that you need him to realize that he has a problem with responsibility. Sometimes, men (and women too) are raised by parents that do not make them responsible for their own behavior. In other words, the parents do everything for the kids, even their homework. So as the child becomes an adult, they think someone else will do everything for them.
Whether or not this was the case with your husband, somewhere along the line he learned not to take responsibility. This absolutely needs addressed either through working on this at home, or better yet, by a therapist. Let your husband know that you want him to go with you to therapy to work on this problem. If he still refuses, then follow through yourself. You need the support to help you decide what to do.
If you decide to leave the marriage, think about a separation first. Sometimes, a separation can help couples think things through and decide what is best for the marriage. Here are some resources to help you with your situation:
Should I Stay Or Go? : How Controlled Separation (CS) Can Save Your Marriage by Lee Raffel
How to Know If It's Time to Go: A 10-Step Reality Test for Your Marriage by Dr. Lawrence Birnbach and Dr. Beverly Hyman
How to Respect an Irresponsible Man, Revised Edition by Christina Dixon and Patricia Hicks
The Emotional Foundations of Loving Relationships by John Hoffman
Try Amazon.com or your local library for these books.
I hope this helped,