This is very terrible and I'm sorry to hear it. It's hard to find the right words to comfort someone when a person close to them passes away, I can imagine it is probably even harder to do so when it is such a tragic situation. Sometimes a person doesn't need words to comfort them but just knowing that you are there for them at any hour of the day is enough, and these are things you can tell him. Tell him you don't know what to say and you wish you could have words to take the pain away. Remind him that you are there for him, and try not to be hurt if he wants space from you as well. Grieving is a process and everyone goes through it differently. As for your parents, I don't know them but I hope they are understanding enough to see that this is a hard time for him, which in turn makes it a hard time for you. Telling them that you would like to be there to support and comfort your boyfriend when he needs you the most is important to you.