In this day and age, sometimes it's the method of communication. I've noticed that there are many folks that will email, text or use Facebook messaging (or other types of messaging that I'm not familiar with) instead of talking. They will "say" things more readily in a text or IM than they will face to face.
Now, given what you've said, I have no idea if your Dad does any of those things, but maybe it's worth a shot. As Mossroad mentioned, have you told him? That's a tough conversation to have, because there is always the fear that he may not reciprocate. But as they say, at the end of your life, you will more often than not regret the things that you DIDN'T do, more than things you DID do. Don't let this be something you didn't do, if it is that important to you.
If you give your full measure, and it still doesn't go anywhere, than at least your conscience is clear and you know you did the best that you could.
Hope things work out for you. Good luck and take care.