I believe love does not stop; however, caring for someone can. Sometimes we put too much time and energy into people who do not appreciate it or reciprocate it. Some people push and push until we have to give in and acknowledge we can love that person but we cannot continue to revolve our world Round him/her.
Grandpa doesn't feel comfortable leaving the place he's grown up in and has to be almost unconscious to go. One of the reasons for Grandma and Grandpa's deaths could have been from the new environment and not being able to adapt to it (Steinbeck 111, 146).