Well, then you are doing what you can do. All you can do is 100% of your part and become someone only a fool would leave. Then, if he chooses to get a D, it's on him, and perhaps you are actually better off...
Im starting to think that my H is not actually capable of the self-reflection, empathy and capacity for change that is required to have a successful relationship. He thinks it was "us" that was just a bad combination. That may be true... but that doesn't mean the problem is "me", if that makes sense.
If your husband walks away, it doesn't mean the problem is "you".
I can also see from your signature that you have been together since you were quite young, had children quite young, and are still relatively young. I have noticed a bit of a pattern on this board that there are a lot of young couples in crisis. I wonder if part of the issue is that we are still growing and changing so much during our 20 s. It's hard to be a great spouse when we are still figuring out who we are (and have to learn to be a parent at the same time). That doesn't mean this won't be a powerful (and positive) growth experience for you... you can find resilience, maturity, and who/what you truly want out of life through this process.