raising Avons affection as much as you can liking background music not judging him when he shows you the pictures you can tell when he hates something you say his expression on his face will show it agree with everything Avon says until it's more then 3 options then it gets complicated for the snacks asks what he'd want then chose from those etc you gotta actually talk to him without boring him which is stuff he wants to hear call him cemetery boy and hot grimreaper etc.
This ending is like he loves you forever but ends up killing you to stay with you idk it's weird
You didn't get enough affection for him to actually like you so that's your issue pay attention to his facial features.