Is it normal to not mind being used in this case
Let's say you've had a friend for years and they have serious depression, but get temporary relief by being with you.
You try to be there whenever they need you, even if it means being pushed to your limits - going nights without any sleep while also having work and school, avoiding others, worrying yourself sick (literally) whenever you don't hear from them, and generally being stressed; even though you know they would not do the same for you and probably don't even care, due to their mental illness.
Would you consider this as being used, and is it normal to not mind if it is because you know they probably feel way worse?