he'd do that, too.

[Maybo]

You can't take credit for sobering him up, because he did that. And if he starts drinking again, you can't take the blame, because he'd do that, too.

Source: Fairy Tale by Stephen King

What does "he'd do that, too" mean? He would take the blame or start drinking again"?

 

[emsr2d2]

In the same way that "he did that" refers to his getting sober at the start, "he'd do that" refers to his starting drinking again. The speaker is basically saying that "he" is solely responsible for their alcoholism and their sobriety.