How do you tell your depressed girlfriend that you want to break up and be with someone else?

i would never cheat on her, but how do i tell her i want to break up when she is suffering from depression? i don't think its fair for either of us that i stay in this relationship only because she is depressed and i feel sorry for her. How do you tell your depressed girlfriend that you want to break up and be with someone else?
i think thats probably true, as long as you're not dumping her BECAUSE she's depressed coz this is probably the time she needs you most. .. though i suppose its not really fair on you whatever the situation is. i suggest you do it gently face to face, and don't mention this 'someone else'. and try and be a friend to her after you break up, im sure its what she needs at the moment more than anything else