No one has a psycho SIDE (where one part is acceptable and another part that is not). A person is either psycho or they aren't. That means that a sane person is NEVER [allowed to be] psycho. His violent psychotic behavior is the kind of person he is. He feels free to be "psycho" with you because he knows that are not going to break every bone in his body (he would like to be that way all the time, but he knows that he would either end up in jail or dead). Not only is your life at stake, but the lives of your children also, if you have any. The deadly situation is real, the psycho situation is real. No human being would ever talk freely about killing someone else (especially if one is already deceased) unless they were psychotically dangerous (not just insane, but a killer). More than that, he says this as part of a LOVE relationship????? You have been psychologically conditioned to think of all of this as normal (sane),...IT CERTAINLY IS NOT!
Whether anyone would try to convince you that he can change or not (yes, a team of navy seals could possibly change him after 5 years, I doubt it, he is one step away from being a serial killer), he will not change. The question should be...WILL he change? The answer is NO because you can't make him change. Alert family and relatives, alert the police and a good lawyer, get a dog that is capable of being a threat to your husband whenever your husband becomes a threat to you (be good friends to the dog and don't let your husband be a better one), and if possible get an electronic alarm system that will call the authorities whenever there is trouble, but remember, he CANNOT change, he is a killer and has a killer's mind (he may already be wanted by the police and just never got caught because he changed his identity), he is not just a 'meanie', he speaks of "killing".
The reason evil has been happening repeatedly since time began is that excuses were made that it should not be considered 'unacceptable', bad, undesirable, etc. Your husband also gives you EXCUSES (keep your mind straight and don't let him convince you that his behavior is "OK"). You are being psychologically conditioned (trained) to accept his abuse (he is glad you are being a good little soldier and letting yourself be brainwashed). You are starting to learn guilt and shame very well. You wrote...
"feeling completely worthless and incompetent and completely, stark crazy".
A truly and completely depressed person cannot realize their sorry state (situation) as easily and clearly as you do (I think that you are sad and depressed that you are in a depressing situation, but don't let him convince you that are mentally unstable, his behavior is not your fault and you do not deserve it). You are not MAKING a "BIG DEAL", it is a "big deal".
"why are you making such a big deal, just be happy and get over your depressed state. He shouldn't determine how you feel, shake it off, when you exhibit your weakness, that is when he attacks, the problem starts with you" .... Can he change? What are the chances? When we talk about these things, he is sincerely remorseful, it is as if he can't control himself when his ire overcomes him and he becomes downright frightening".
Do not shake it off (it is a big deal), do not GET OVER IT (don't brush it off, it's serious). Of course he shouldn't be causing you to feel this way (no husband should). In ANY friendly relationship (especially a romantic one), there should be no exploitation of the other person's weakness, in fact, any weakness might be viewed with fondness. Keep your head straight, the first thing he does is train you psychologically to accept shame, guilt, humiliation, intimidation, abuse and low self-esteem so that you will allow abuse.
He is not SINCERELY remorseful (he wants you to think he is, he also wants to think he is, this way he can think good of himself, he needs you to feel guilty enough to forgive him and justify his behavior). He does need you (to accept his guilt and to allow him to feel as though he is a good person,..whether anybody else does or not, he doesn't feel like a good person because the truth is,...he is NOT).
Visit the NARCISSISM forum, he is not just a narcissist (he speaks of "killing", he's a killer), but you will learn how he has psychologically conditioned you.