The thing you need first Ender, is some type of support, whether it is a friend, family member, a therapist/psychiatrist, etc., to discuss this situation. In my opinion you should attempt to get a therapist/psychiatrist
as soon as possible. You need more perspective about this problem than most of us here can offer. We can support you with advice, but you need to take steps to make sure your partner receives treatment with a qualified mental health specialist.
I think Bowyn's post sounded fairly accurate and he has given you very good advice. There are many therapists/psychiatrists who will be willing to work on a sliding scale. My own therapist is a nurse practitioner who works for/with a psychiatrist, thus she is able to prescribe psycho-active medications for various medical problems. In any case, seek support/counseling as soon as you possibly can. There are options available, but you must be willing to take the time to research where those options lay. Get online and get telephone numbers. Start calling offices. Don't put off this course of action if he has soothing explanations or you feel that this situation will get better. I believe either scenario is a mistake.
Your partner does sound like he may be suffering from some form of PTSD. Dependent upon the abuse he suffered, he may be associating an immediate situation - whether just talking or an escalation to argument, even one that stems from what seems like nothing at all to you - with some event in his past, whereupon he strikes out first as a defense mechanism. This may be his default behavior when faced with a situation he feels powerless about, when he may feel like you are not understanding his needs, or when he feels you are not listening to him. Possibly he is instantly reacting by reflex to an event from his past.
Remember, I'm only guessing here. I don't know him and I haven't the skill set to diagnose any particular problem. I can only give you advice based upon your original and subsequent posts.
It is possible that I may be over reaching here, but I also think your partner
could be suffering from a bipolar disorder, which is something I am particularly familiar with. There were many familiar patterns of behavior that I identified with from your initial description of the situation. Especially when you write that many days or weeks, would pass and he exhibited little or no irrational behavior.
Bipolar disorder is often characterized by emotional highs and lows. Depressed behavior (which people often successfully hide) may appear only as a subdued state and can occur for days or weeks at a time. This state of mind has symptoms such as low energy, little drive to participate with activities, extended periods of inactivity, decreased interest in hobbies or accomplishing daily function, etc.
If such depression is followed by moments or days of unexpected anxiety (which often manifest as anger - such behavior is characterized by irrational moods, inconsistent thinking patterns, unexpected outbursts of emotion, heightened vocal outbursts, physical rages,etc.) this
may indicate bipolar disorder.
This link to the Mayo Clinic may be helpful for you to understand bipolar disorder:
Bipolar Disorder symptoms and causes.
This link, also to Mayo Clinic, may shed more light on PTSD for you as well:
PTSD symptoms and causes
I suffer both disorders, so please don't think one condition precludes the other. Either of these issues, from which he may or may not suffer,
are only guesses my my part. Nothing takes the place of a professional opinion by a qualified medical physician.
In any case,
physical abuse is not acceptable. I understand that you don't know how to extricate him from your life and I understand that you probably don't want to give up this relationship. There may, however, be no alternative to breaking up. You must accept that there may come a point when it is necessary to leave him at a moments notice. You should have a plan including a safe place to stay, a means to call for help, transportation away from him, etc. You cannot be afraid to call the police if it becomes necessary.
First and foremost your well being is the paramount issue.
Find a therapist for him and make him aware that in order to continue your relationship with him therapy is required. Make sure when you deliver this news that you are not alone. Help, if only in the next room, must be available if the situation becomes volatile. I would strongly consider therapy for yourself as well. Both of you have been affected by what you describe is a dysfunctional relationship and as such you need someone, even if it is only for a short period of time, to help sort out your feelings and provide some much needed perspective.
While I would never condone physical abuse, I do advocate each of you understanding the other person and the issues which have brought you both to this place in your relationship.
The hard truth is that you may have to abandon this relationship. If it were me I would first attempt to discover the cause for his behavior. Additionally it must be made clear to him that physical abuse is off the table and grounds for separation. If his condition is medical and treatable, then you must decide if you are equal to the task of remaining with him. Believe me when I tell you that being in a long term relationship with someone who has psychological issues is not an easy road to travel. It requires tenacity and abundant patience. Leaving this relationship may be your best option.
Unless it is an emergent situation, I would not want to leave him, always wondering and having this "If I'd only just..." type of regret, without a qualified medical opinion. You need to have the facts and options placed before you to make a rational decision.
Needless to say that threats to your life must come before your relationship. If you must, leave.