Bernard wanted to break this habit after all, why couldn't a chair be used as a chair?
I know this example is a run-on sentence but I want to know if I can fix it by putting a period after habit and capitalizing after?
Yes.
Yes, you can certainly fix the run-on sentence by placing a period after "habit" and capitalizing the first letter of the following word. By doing so, you would create two separate sentences: "Bernard wanted to break this habit after all. Why couldn't a chair be used as a chair?"
Breaking down the sentence, the first part states Bernard's intention to quit a certain habit. The second part of the sentence poses a question about the functionality of a chair. By making these two distinct statements, you provide clarity and improve the overall readability of the text.