Whether or not you should stay in this relationship depends on how you feel and your boyfriend's ability to manage his anger in a more suitable way.
Look at your situation and ask yourself if you are willing to settle for this. Be honest with yourself about what happened -- is it possible for your boyfriend to change and are you willing to work through this, or would it be in your best interest to leave the relationship in the past and move on?
The first step is to put your feelings in perspective and talk through what went on and what needs to change in order for you to feel safe in this relationship. Make an agreement about what you expect from the relationship. You should tell your boyfriend that although his intentions in defending you against his friend were good, you got hurt in the process and that is not acceptable.
Anger is a healthy emotion, but when it becomes uncontrolled and violent it can cause problems. There are choices as to how to deal with anger. In any situation, your boyfriend has the ability to control his feelings and deal with them in a way that no one gets hurt. If you ever feel that your boyfriend could become violent towards you, do not feel guilty to walk away from the relationship.
Every relationship teaches you something and helps you to grow as an individual. It is natural for a relationship to have its share of problems; sometimes things can be resolved and sometimes it is best to go your separate ways.
While trust might be an issue at the most, it is not an impossible obstacle to overcome when two people really care for one another.
What type of relationship do you have? A relationship is based on the needs of two people. A good relationship has respect, honesty, understanding, acceptance, appreciation, communication, sincerity and genuine love. You should be able express your concerns and emotions to the other person in a good relationship. You might disagree or argue sometimes, but you should be able to communicate and reach a compromise. Bad relationships have the opposite traits of a good relationship and make you feel bad about yourself and are chronically lacking in what one or both partners need. There is little common ground, no significant communication and almost no enjoyment of each other.
If someone treats you badly then they are not a suitable partner. Remember that you always deserve to be in a relationship where the other person respects your feelings and treats you well. Do not stay in a bad relationship with the false hope that your boyfriend will change. If you feel that you have given this relationship all you have and are not getting the same in return or you feel unsafe in the relationship then it would be best to leave the relationship.
If you decide that you want to give your relationship one last chance you both need to acknowledge the mistakes of the past that caused your problems and learn from them. Find ways of resolving your issues; talk through the issues that are causing your uncertainty in this relationship and what needs to change to make the relationship work. It's perfectly reasonable for a couple to get back together if they both change and once again become compatible.
It really seems like your boyfriend is content with the way things are now, otherwise he would have changed. You are not getting what you want from this relationship and you have a choice. You need to talk with your boyfriend and come to a more final decision about the status of your relationship. If he wants a committed relationship with you he is going to have to change his behavior NOW, plain and simple. Put your limits in place and follow through on them.
There is nothing more you can do except to choose a direction that is more emotionally satisfying. You may walk away from this relationship with clearer ideas of what sort of qualities you want or don't want in a partner. You might want to continue the relationship and work out your problems, maintain a friendship or even continue taking some time off from the relationship (because an entire year has already passed, I would not suggest this course of action for you). Whatever you decide, remember to always trust your instincts and do what is best for you.