First, you are showing courage by asking for forgiveness. So, please realize this. Second, your boyfriend is near the beginning of the forgiving process (anger is part of the beginning) while you are very far along on the seeking-forgiveness path. Please see this discrepancy between where you are on your path and where he is on his path. There is nothing wrong with both of you being at different places on your respective paths.
I would urge you to be patient with him and see that he is just at the beginning of forgiving. It will help if you express understanding to him. Let him know that his forgiving is his choice.
When you see that his heart is soft toward you, gently—gently—bring up again the idea of his forgiving, with the addition that you know it is his choice and that you are willing to wait for him to get used to the idea of forgiveness.
With time and perseverance, he is likely to join you in the process of seeking and granting forgiveness.