Why did Proctor have the affair and what prompted him to end his affair with Abigail?

From the text, we can infer that Proctor began his affair with Abigail because he was looking for something that he wasn't getting from Elizabeth.... whether is was purely physical or romantic, we are not told. Proctor's ending of the affair is likely a result of conscience.... doing the right thing, although, in the end, we come to realize that Proctor does, in fact, love his wife.