You know what, big applauses to him for being the only known mc (as far as I’m concerned) that did it with an actual spider. No half-species, like a “spidergirl”, or some other inbetween, but a literal spider.
Well, I mean, she was in human form. If anything his human girlfriend was more of a monster than the spider. Also we don't know if the girl is the primary form or the spider or they're both equally "her". We don't know if the human is fake or not.
She showed him the spider form then transformed into a human and fucked him. Shit happens.
Also how is she getting so much blood from him without him dying? The hell? All those bloodbags and getting sucked daily, that's alot.