I’m sorry this is so hard for you. The most important relationship in your life is with your boyfriend. But the most important relationship in his right now is with his deceased brother. This is a normal part of the grieving process, although for it to be this intense after a year might be a concern. Without knowing the specifics of what happened, I can only guess that he is having trouble making sense of the early death of his brother and he may be wondering how he can go on with the life his brother didn’t get to have.
What he doesn’t need are demands – even from the young woman who loves him. From his point of view, being upset about your relationship is small stuff. He’s dealing with the much larger issues of life and death.
My advice to you is to let him know you are there for him but don’t push him to talk. Since it’s been over a year since his brother’s passing, it might be helpful for you to locate a therapist who specializes in grief counseling and gently encourage him to go. If you think he has a good relationship with his parents, it might also be helpful if you shared your concerns with them. It’s important for your boyfriend to know he is not alone in his grief and to have the support of others who share it.
Your relationship is going to be less important to him than to you for awhile. He may need more time than you can tolerate. In that case, the most loving thing you can do is to take a break without any blaming. He’s doing the best he can. But you may need more than he is able to give.
I wish you well.