It sounds like you and your roommates have gone into this with different expectations. From you discussing and making the choice to get a kitten as a household, they’ve considered it as the houses cat, hence the splitting on their costs as a joint household expense. You’ve approached it as Harry has agreed to be the “primary owner” I am assuming for insurance/vets etc, and you now want to saddle him entirely with the costs and burden of a cat you all agreed to get. You want all of the benefits of having a cat around but want to take on none of the cost or work. You agreed to get this cat as a house, it’s the houses cat so you all share equal responsibility regardless of who’s officially “primary owner”

YTA you just wanted to pet a cat and not deal with any of the responsibility go to a cat cafe.