If you say that you could do without something, you mean that you would prefer not to have it or it is of no benefit to you. He could do without her rhetorical questions at five o'clock in the morning
If you do without something you need, want, or usually have, you are able to survive, continue, or succeed although you do not have it. We can't do without the help of your organisation We've had a bit more money and that, and the baby doesn't do without