Shadows, every sympathy.
Do you have any siblings? Does your father look at them with the same hatred sometimes?
How is he with other people? does this hatred surface there too in any form? does he take out his anger at one person on others too? What I'm getting at is, are you the only person he looks at like this? if you are, then it could be significant. If he looks at other people like that or takes out his anger on others then well, you may just have a father who isn't always that nice.
If you really are unsure if your Dad is your Dad, it's a really difficult one. On one hand it's really hard living with a worm of uncertainty to the end of your life. But equally sometimes some dogs are best left sleeping .....
Do you like the family friend? how would you feel if he did turn out to be your bio. dad?
To my mind the person who brings you up is your parent. Certainly the parent in your heart, the parent of your childhood, the one you love. Having said that the blood link with a bio. parent is there for some people. If the parent-in-your-heart turns into a sod who inflicts a lot of hurt, then the bio. parent can be someone to turn to even though they will never be the same as the parent-of-your-childhood.
If your Dad didn't look at you with hatred sometimes, then I'd give slightly different advice here. But since he does, I think very cautiously you need to consider getting a DNA test done but possibly not until you have left home. If you discover that you aren't his daughter it is a gigantic upheaval that will stay with you life long, and it could make living there very hard.
I've asked a lot of questions mostly to get you thinking about how you would handle either result, and also how you will handle the uncertainty if you choose not to get a test. Some people can live with it, some can't. Whatever you choose, I'd suggest taking a few hairs from your Dad's hairbrush and secreting them for future in case you do decide to go for a test.
Wishing you the best and peace; and that whatever the situation turns out to be, your Dad gets a grip and stops looking at you like that. He shouldn't. It isn't right.