Oh come on why are u angry with the Fox honestly I feel sad for the Fox because it obviously he was in love with the grandfather but the grandfather went and get married and he didn't want to destroy the grandfather happiness, it's obviously he like kiyo now but he feel kiyo will be just like his grandfather, honestly if he really did leave then that is understandable because who would want to see a person they like leave them for another again that would be painful so he thought he should leave first to avoid getting hurt again
I think he wasn't in love with the grandfather....more like indebted to his generosity. He did say he was happy when the grandfather got married but in Kiyo's case he got extremely jealous and mad. I think he's just afraid of losing Kiyo cause of immortality and god shit stuff.
yo.
if you just left a note and bolted on my sweet little boy, i'm gong to SHAVE ALL YOUR FUR off of you!!!