Alastor is so consistently human and trusting because of/around Rosie that it's almost uncomfortable to watch... general overconfidence to a fault + trust in a specific person is surely a weird combo. because at least otherwise the overconfidence is buffered by mistrust (i.e., he thinks "yeah, I can beat EVERYONE up if they attack me! I simply can't lose!", not "surely nobody wants to hurt me here, that'd be impossible"). especially weird to see him enjoying some bits of Don't You Forget. I mean, the name of the song and Rosie's message track - even in the middle of it, he seems to be occasionally forgetting its purpose, lmao.
It's like he thinks "Rosie" (or at least "contract with Rosie") and gets drunk on that alone. dude doesn't need substances