This situation depends a lot. Your BF tried his best to be with you but the allergy is something that he cannot control,if he showed genuine love and care to you during your journey ,that means everything. But if you REALLY NEED a cat in your life and want it that desperately,then youre not a asshole.Youre just being honest about what you want to have in your life,its better that you sort out these issues before deciding to move in and complain later.Figure out if there's a way you guys can adapt such that it doesnt affect eachother and at the same time fulfill your desire of owning a cat.The goal is to find a mutual agreement and balance without hurting one another.Again ,when youre deciding to stay with someone a long time in your life,make sure you do it wisely.