Hey Ali, The sentence that most sounds like a true native speaking is the second one ''I love you more than he does''. If you were to write someone a letter or even to express your feelings to a person, then you should consider being a little more formal by choosing the first sentence ''I love you more than he loves you.'' Hope that helps!!!

The second one is the more native one :) I love you more than he does.

As others have said, you **might** hear the second sentence more often but, as my father used to say, "Just because everyone is walking off a bridge doesn't mean you have to do it." However, while instructing classes in Rhetoric and Argumentation at a university, I would teach that the parallel construction of the first sentence was more influential than the form of the second sentence. Substituting the word "does" for the word "love" in the second half of the second sentence requires work on the listener's part to figure out "what" "he does". It's not a difficult thing to figure out, but the "question" is there.