The narrator of Tess of the D'Urbervilles gives us what critics call a "sympathetic inside view" of only two or three characters: Tess (of course), Angel, and, sometimes, Alec. We're frequently allowed to see what Tess and Angel are thinking and feeling – sometimes the narrator even explains why they're feeling what they are, when they themselves don't know.
Alec is a tougher case. The narrator doesn't usually give us an inside view, because Alec isn't a sympathetic character and it's a lot harder to view someone as just a bad guy when you know exactly where he's coming from. But although Alec is the bad guy, he's also human – Hardy doesn't want anything about the novel to be black and white. So the fact that he's willing to hint at Alec's thoughts and feelings makes it that much harder to judge Alec as harshly as we might want to.