I think that although you dad won't talk about his feelings, as long as you are there for him if he ever needs to talk, then that's the most important thing.
It is times like this you think about those close to you, and imagine what your life will be like without them, it's what everybody thinks, I guess it's the way humans ponder their own mortality.
So please don't think you are alone, I think everybody has felt that way, it's part of life.
You just have to make sure your father doesn't feel alone, and at least offer him some help, inviting him around for dinner etc, helping him out, letting him know you are there for him.
People deal with things in different ways, I'm sure if he ever felt the need to open up he would, and that person would probably be you.
I hope you start to feel a bit better soon, which I'm sure you will.
Hugs from Jack & Sunny to make you feel a bit better