I somewhere read a line about the relationship of two people. I'm looking for the exact words. It was something about one being like a stray dog, that you hate him, but you feed him because you think otherwise it's on you if he dies. I couldn't find it anywhere on the web. Thanks!
The proverb collections I consulted do not list any sayings about feeding a stray dog. But a Google Books search turns up a number of matches for sayings that convey essentially the same idea—that feeding a stray ensures that it will come back for more. A less common extension of that idea is that the feeder becomes the stray's benefactor for life.
From Stormie Omartian, Step in the Right Direction: Your Guide to Inner Happiness (1993):
If you feed a stray dog, he's going to stay.
From C. Michael Davis, Don't Pet the Dragon (2006):
Momma always had left-over biscuits and I soon figured out that once you feed a stray dog you couldn't run him off with a stick.
From Ann Weisgarber, The Personal History of Rachel DuPree: A Novel (2010):
They're like stray dogs. Once you give them a scrap, they never leave.
From Crystal McDaniel, Predestined to Reign: For a Time Such as This (2010):
Just like the saying goes: "You feed a stray dog, he will keep showing back up at your house."
From Raymon McAdaragh, Developmental Harmonization (2011):
Negative thoughts are like stray dogs; if you feed them, they will come back; if you continue to feed and entertain them, they will stay, while enticing your behavior with their negativity.
From George Lindsay, Mesa Flats Resort Circles the Wagons (2012):
Once you feed a stray dog, he's yours for life.
From Sandra Kring, A Life of Bright Ideas: A Novel (2012):
When people say don't feed a stray dog because then they won't go away, they're telling the truth.
From Paul Jordan, Easy Day Was Yesterday: The Extreme Life of An SAS Soldier (2013):
You know what it's like when you feed a stray dog — not that I'm comparing the lunatic to a dog — but when you feed a stray dog it decides you are now its best friend and hangs around for attention and more food.
From Ray Wooster, A Boy's War Journal (2014):
If you feed a stray dog and lavish it with affection, it's yours for life.
T.J. Lorenzo, How to Rescue a Drowning Heart: MM Romance (2017):
When you feed a stray dog, he'll just keep coming back for more.
Given how many matches the Google Books search finds (these ten and others besides), it's somewhat surprising that most of them were published in the past ten years. It's as though the saying is in the process of growing into a proverb.
On a related topic, an interesting note on feeding strays appears in Frank Maraist & Thomas Galligan, Louisiana Tort Law (2016):
Cf. Terral v, Louisiana Farm Bureau ...(La. App. 2d Cir. 2005) (person who takes possession of a stray dog by regularly feeding it over a significant period of time assumes responsibility for the dog's welfare; such conduct is enough to impose liability on the person under La. Civ. Code art. 2321).
So be careful. What begins as charity may become an obligation.