Ah, apparently your dad loves you and might be a teeny bit intimated that you seem to be rejecting your background - of which he's probably a very big part. Go easy on him, keep a sense of humor, make home some tasty vegan treats to share, and reassure him you'll always love him. In time, everything will sort itself out. Don't preach, don't let a wedge come between you, and remind him of all the other ways you and he agree. Good luck!
Such wisdom in this post!
I can think of three main reasons that a parent would be against their child's going vegan:
(1) As Poppy and others have noted, it may seem to him that you are rejecting your family's collective background, his parental wisdom as it were.
(2) He may be worried that a vegan diet is not healthy.
(3) A parent may be annoyed about having to buy (and prepare) food items separate from what the rest of the family eats.
I am going to concentrate on # 2, here. If you have the ability to watch a streaming video with your dad, either on your TV or on your computer, see if you can talk him into watching a couple of the following. They are all by physicians, all are fairly short, and all describe how a well-planned, whole-food, plant-based diet is the optimum one for good health:
Dr. Joel Fuhrman: http://www.drfuhrman.com/default.aspx
(See his wonderful, short video, “I Love Nutritional Science”, on YouTube at the following (shortened) link: http://tinyurl.com/oo5vvlt
Dr. Dean Ornish: http://deanornish.com/
(See his wonderful, short video, “Seven Billion Well”, on YouTube at the following (shortened) link: http://tinyurl.com/z2nya69
Dr. John McDougall: https://www.drmcdougall.com/
(See his wonderful, short video, “The Food We Were Born to Eat”, on YouTube at the following (shortened) link: http://tinyurl.com/njropdj
Dr. Caldwell Esselstyn: http://www.dresselstyn.com/site/
(See his wonderful, short video, “Making Heart Attacks History”, on YouTube at the following (shortened) link: http://tinyurl.com/pn2jth6