First off, the only reason this counts as a 'game' is because you get to *kind of* (very loosely) choose what porn you want to watch through the choices in where to go in the house. Regardless, these 'choices' don't mean anything, and don't actually influence the story at all.
tl;dr this isn't a CYOA, nor a basic rpg, it's a story that is attempting to masquerade itself as a game.
If this was given as a collection of ntr porn videos, I'd have given it a 3 for doing its job. However, as a html game made in twine, this leaves a lot to be desired. The hardest part of creating this must've been finding the porn. I've used Twine before to a very small capacity. This is neither technically amazing, nor is it anything past what a twenty minute read on the documentation will allow you to do.
Furthermore, the story leaves a lot to be desired as well. Don't get me wrong, I'm not an avid fan of ntr. Regardless, even I know the importance of story in such a fetish, and this 'game' has basically none. The main character has no character (this is somewhat excusable considering that nature of this sort of genre). The girlfriend quickly turns from 'oh I love you babe, I love how you fuck my feet' to 'MhmmM, I loVe BlAcK CoCk' in the matter of a single day (between 3 to 4 or some shit). It's just 8 (?) days of porn slideshows.
The lack of choice, the lack of story, the lack of any sense of technicality sees this as a barebones 'game'. I would not recommend this. Read some literature if you want better story. Watch some porn (ntr) if you want to have story that's better than what is given here and you want to fap. Just don't look to this .html + images concoction.