There is no third state; a law is either constitutional or unconstitutional. A legal verdict rendered in a proper court hearing should be based on a fair hearing of the evidence. Courts and juries get to decide cases and an allegation of abuse as justification for homicide must comply with the particular state law which must , in turn, comply with constitutional standards.
Apparently, I'm not communicating well. Juries do consider other factors besides the Constitution, and they should. That doesn't make their decision unconstitutional, but it's also not a decision that is required by the Constitution. At least in my state, abuse, even if proven, does not justify homicide. Killing an abuser in his sleep is legally homicide. My point is that regardless of what the law says, abuse should be taken into account in sentencing, even if the killing does not meet the standards for justifiable homicide or for self-defense. Not all murders deserve life without parole, but some do, and it's the considerations that are neither in the Constitution nor prohibited by the Constitution that control all of these decisions.