This is one of those questions where the answer depends on the individuals involved. There is no yes or no answer from the standpoint of (people in general).
Personally it would be a major challenge for me to stay upbeat, positive, and romantic while being involved with someone who is clinically depressed.
At best all you can do is help them research the illness and get into therapy or possibly find the right meds. However much of what needs to take place will have to be driven by the person who is suffering.
I tend to subscribe to the old Neville Brothers song; "When something is wrong with my baby, something is wrong with me". It would be extremely difficult for me to be "happy" if my significant other were down in the dumps.