You would know better than anyone here what abilities your boyfriend has. He has the ability to sue his roommates for the value of any discarded property. Did you really not know that? Presumably, he also has the ability to find a different living situation -- either on his own or with roommates who will be more respectful of his property.
There's no "we" here. As you told the story, this has nothing to do with you. Your boyfriend's landlord is legally free not to renew the lease for the reason stated (which appears to be that the landlord considers him to be a pain in the butt).

