How do we tell our roommates we re moving out?

My boyfriend and I signed a lease in march with a married couple, the male roommate (let s call him A) is my boyfriend s best friend. Over the last 7 months there ve been lots of problems in the house, specifically between my boyfriend and A, as well as pet behaviour problems with my cat peeing all over A s stuff and A s dog peeing all over the house. We re not planning to cut the lease short or anything (even though just a couple months ago we really thought we were going to have to), but they sound like they re expecting us to sign another year with them. My thought was, since A is very self absorbed and will likely verbally attack my boyfriend and myself (ex. that s childish you can t afford that), that we should make it seem like us going our separate ways will benefit A more than cause problems. Does that sound like it might work? The only thing that really sucks is that their cat and my cat have become best friends, and I really enjoy living with this other girl.