I'm sorry to hear of your husband's diagnosis and behavior changes that were negative. Since his diagnosis and medications it sounds as if things are improving and giving you hope that at some point he will return to closer to his former self. Do you know the cause of his issues, i.e., did he have an accident or some other incident that was at the base of his OCD, Bi-polar, Epilepsy and brain injury? How long has he had these issues?
I understand your wanting to know if his mood swings and intense feelings and behaviors will get better. His doctors are the best people to answer those questions. I have dealt with family members who have mental illness issues, and I know it's difficult to do over the long run. No matter how much you love the person, you can tire of dealing with the repetitive issues that you thought were "better." There is probably no guarantee that your husband will continue to improve over time, any more than any "normal" people have a guarantee that they will be stable and improve in life. That said, there's not necessarily any promise that he won't get better either. So, hope is warranted.
As his caregiver you may push your own emotions down in order not to upset your husband. At some point those emotions tend to bubble up into full blown anger that needs to be released. I highly recommend counseling for yourself so you can learn how to take care of your emotions and set boundaries for yourself. A good place to start is with a support group that has members dealing with the same things you are. Many hospitals offer these group meetings at no cost to caregivers and family members. Start there, but also seek out individual counseling for yourself. I was able to manage and express my own feelings constructively after learning how in my therapy sessions. You cannot change your husband's behavior or feelings, only he can do that if he is medically able. The only emotions and behavior you are in control of are your own.
Good luck to you and your husband as he recovers. Please keep us in the loop as you work through these difficult, yet promising times in your marriage.