I hope you put your agreement in writing.Just for information: If you accept rent late, your behavior waives your right to any late fees or ability to enforce rent due on time.You can re-establish your deadline for rent, by giving notice in writing with 30 days notice.  

It's a miracle they didn't burn the place down, as it was apparent that they just dropped cigarettes regularly, that just burned themselves out on the carpet.So, did the co-signer change the risk/behavior of the tenant who wouldn't qualify without one?  

The issue I am exploring is not my feelings about alleged bad behavior but my legitimate responsibility.

Their behavior is indicative of deeper issues.  

I have wondered it there was something about my behavior.

Why else would would you attempt to justify such bad behavior?

Then, maybe you can get them out for criminal behavior?

I seriously believe she has some sort of obsessive disorder or something, but maybe a letter from an attorney might correct the behavior.

., you don't have to rent to them.You deny based on behavior and ability to pay - not they "type" of disability they have.  

Not all terminations are because of poor behavior by one of the parties.