If you go out to a restaurant and see how that person treats the wait staff.
If you go to that person’s family home and see how they treat their parents/siblings/grandparents etc.
If you encounter a lost or injured pet, you check that person’s reaction (do they want to help or do they not care)
You encounter a friend or relative who is down on his luck and you check that person’s reaction (and reasoning) as to whether they will help or not.
You want to invite a group of your family members or your friends over to spend some time with your SO, you check his reaction. Is he happy to meet them, ambivalent, angry?
You get sick (not from being drunk, but ill) and need someone to help you go to the bathroom and help you to eat and possibly to help rub your back or your feet if you are in a lot of pain, you check their reaction. Do they jump in automatically without question to help you, do they act all squeamish and grossed out and not help you, or do they not help you because it doesn’t occur to them, or do they help you, but complain about it, or do they help you, but only in the minimalist of ways without actually making you feel better?
Do they let you know where they are going to be without making you feel guilty for needing/wanting to know where they are going to be?
Do they pay attention to the small things that you have said or pointed out and then act on them in sweet ways? Or do they not even pay attention to things that you have said or pointed out that were clear and obvious?