How do I tell my roommate I don't want to live with her next year?

I don't want to live with my roommate next year. When we moved in together she brought one cat but then I went home for one weekend she got another cat without asking me! I'm not scared or allergic to cats but it just feels like cats are taking over our small apartment and it makes me uncomfortable. My roommate also can barely pay for the cats and they sit there all day trying to get more food, she doesn't clear the litter box regularly and she lets the cats lick of plates and bowls. Other than that she a pretty good roommate but I know she'll never get rid of her cats (nor would I tell her she had to) What's the nicest way to tell her I don't want to continue living with her?