AMott, welcome to Psych Central (PC). Sorry to hear your friend and you are experiencing these outbursts. That can be very unnerving and sometimes downright scary.
Does your friend want to get help?
To get a diagnosis your friend would have to go to a psychiatrist or therapist not just once but over a period of time.
If they are willing to enter into some kind of therapy, or even couple therapy might be a start, then progress is possible.
If he does not want to even talk about anything as an option, you have an uphill battle. Psychology is not like surgery. You don't easily remove the root cause of the problem. Without a willing partner, a psychiatrist or therapist is hard pressed to proceed at all.'
Now you could read the forums and maybe find some comfort in reading about other people's situations and find some solace in that.
A word of warning that I hope is never needed, if he hits you or hurts you in a fit of rage, please seek a safe place. Once abuse starts it rarely stops there and only gets worse. Uncontrolled anger is the beginning of violence. If a person can keep it from ceasing control then violence is avoidable. This is a difficult situation. As much as you want to help consider your own safety if anger turns to physical violence.