First off, let me say I am so sorry for your loss----It is your loss also, b/c this man also meant a lot to you---as well as your boyfriend, whom you love very much.
I can give you a little advice---based on my own experience. My boyfriend's Mom passed away from cancer, 6 years ago this coming up September.
Now granted, it was not sudden, however, the family was not told of the severity of the situation---They were told on a Friday, while she ws hospitalized, to call in Hospice to the house, and she passed away very early the next Tuesday morning, while still in the hospital. My B/F and his sister---really had no idea that she was that bad off, so to them, it was somewhat unexpected. That being said, let me tell you how he dealt with it.
We too, had only been together for about a year and a half at that point. He completely withdrew into his inner self, which is the polar opposite of the person i knew. At first, I was very unsure of how to handle this, as we were 22 and 25 at that time. I finally came to the conclusion, that we all grieve differently--He was dealing with it the only way he knew how----He had also just lost his grandmother, whom he was very close to, the year prior to that, only a month after we started dating----He suffered alot of loss those first couple of years we were together.
And not to give you all my story----This is just background, that I am hoping to help you with----so you can see the similiarities. I finally just had to let him deal with it as he wanted-----So much I wanted him to talk to me, tell me what he was feeling---and that just was not happening. And i finally accepted that----but I am not going to lie----it took him 2 years to really "pull himself together"-----and I really hope that is not the case for you and your boyfriend---But i think in some ways, a depression does set in---and they have to be the one to overcome it.
I think you are doing the right thing---which is not pushing him--but yet, letting him know your are "there" for him. I really empathize with you---i know its so hard to want to be there---and to be afraid you are smothering him---but know you are not.
My B/F was the same way----I was right there with him, through all of the funeral arrangements, the visitations, the funeral itself----and everything that followed. We had just built a home prior to this---and his parents had been a big part of it---His Dad is alive, and his parents were married when she passed away.
And I know exactly where you are coming from, when you ask him, if something is wrong with your relationship---and the answer coming from the "cave"-----I wish i could convey in words how much i know that isn't very reassuring.
I have a feeling, that you are doing everything "right"----and all I can say, is continue to support him, love him, and let him know that its okay, if he doesn't want to talk. Eventually, he will---and if I have said too much of my own situation--I apologize---but it was just too similiar not to explain.
I don't think I can tell you how long it will take----Hopefully it won't take long---and it helps that it's Summer-----It is a beautiful time of year---and sunshine is important for that healing process.
If there is anything else, that I can say, or try to make you feel better, please let me know-----I have a feeling we might have a difference in age---But the loss of a parent is so hard at any age----
Please take care, and I will keep you in my prayers. I am glad you found this board---I kind of wish I had something like this years ago---It might have helped me to "vent" a little back then---I am sure there are plenty of others who have even more advice and helpful info.