
Ok...so the seme is angry about the uke forgetting him???

Yeah, I think that’s the premise, though it seems a bit more complicated than that. The seme lost all sense of safety in an unhappy, unsafe place - the uke was his only sense of family. Seems like the uke denying that he knew the seme during a period of heavy abuse broke what little hope/internal safety the seme had left.
I just turned to a mush reading this cute storyヾ(❀╹◡╹)ノ~.
They're so sweet and pure hearted Awwwww ~ ε=ε=(ノ≧∇≦)ノ