Hi Wisp, and welcome to HW. Your post really got to me, as I lived in a similar situation with a boyfriend with 'rage' issues at the same age as you. As you said, he never abused me, but his family bore the brunt of his extreme and out of control anger that would rear itself quite frequently. Other than that, he was kind, compassionate and sweet. As often happens, after 3 years we went our separate ways for different reasons.
I got him into counselling which was the best thing for him. He was able to understand where his anger came from and why he was so fragile. Therapy did him a world of good, so I think its a great idea that your boyfriend sees a professional, because he must be hurting badly.
If he finds counselling to be beneficial he may start to reduce his anger and have less frequent 'rage' attacks. It sounds like his problems or triggers are family based (as was the case with my ex.) Does he have any other relatives aside from dad that he could live with? Maybe family mediation would work, but its a big call.
Im sorry you are scared, I know this too well. The best thing you can do is be there for him and verbalise your fears- I think you should tell him that you are scared, as he may not realise he is upsetting you indirectly. I would also seek professional help and try help him see the positives in life. He sounds confused, almost overwhelmed.
Its great that you are seeking advice, you obviously love this guy and want to see him at his best- I hope others will be able to give more advice also. Stay strong and good luck with tommorow, keep in touch,
Maz XX