I think you need to look at his life as a whole, and how he treated others. For example was he verbally or emotionally abuse with his boss, his friends, the mailman? If the answer is yes, this is how he acted all the time. It may be the BP maybe not. We all have to hold back and not say what we think at times. This is maturity, and respect for others.
If he was only abusive to you and other family members, that was a choice he made.
It is very difficult at time when bipolar people get irritable, short tempered, etc. But there are ways to deal with this, even if we have to just walk away.
I'm sorry this happened, but you can be free from it if you can practice forgiveness.
Whatever the cause of your treatment, you didn't deserve it, whether it came from an illness, or not.