Basil begging for forgiveness?

Hello guys, I just finished playing Omori for the first time and only did one ending, where I'm saving Basil and stuff, but he keeps talking about forgiveness. What did Basil do that Omori/Sunny has to forgive him? If anything, shouldn't Sunny be apologising? And generally, why is Basil acting like if Sunny leaves him, he'll die or something? Was it because they were super close friends? I want to do the other ending(s) too but the boss fights aren't exactly my favourites so they're kinda pushing me off. Should I finish all endings to understand better?