I don't recall which movie this is. I think this one was only one of the scenes - maybe a side story - with not that much influence in the main plot.
There was an old couple (man & woman, 60+ years old) in a room, watching TV. One of them (I think the man) had memory issues - he was completely alienated, watching TV on the couch all day. The other (I'll asume the woman) needed to take something like insulin shots, which were applied by the man. Each time a clock would ring, the woman would remind him about the shots, hand him the stuff he needed, and apply the shot, smiling because he's helping her spouse.
At some point, the woman started to believe the man was only pretending to have memory problems - or didn't want to believe that he really did have memory problems. To prove it, at shot time, she'd turn the clock backwards after each shot, hoping the man would realize he had already applied that day's dosis. But, as the man kept doing it again and again, she started crying, probably deciding she'd rather die from overdose than living with the fact that he actually did have memory problems.
Do you know it? I can't recall anything from the main plot, and it would be really weird if I made all this scene up. I really think it's a very well known movie (Hollywood, probably from the 90's or newer), but have no evidence to support that.