Maybe what you need to hear first here is that you are heard, that you are understood, that others find all this as sick and fucked up as you do. If so, you got it bro. We have all asked these questions or others like them.
Maybe this will sound almost too obvious to be worth saying, but the answer to your questions would all fall under the heading of "distorted thinking". Abusers justify what they do with all kinds of explanations, but all of them are false excuses, not real reasons. For example, they will trick, deceive, pressure and threaten a boy, and then when they get what they want they will say, "I only did what HE wanted."
I want to comment just for a moment on your closing thought:
god i have a million more questions that i'll never get answers too, but i'll keep asking them anyways
Yep, keep asking! This is what you should be doing. Whether you get answers or not, you are saying, "This is fucking me up big-time. Please help." Keep asking for the support you need. That's what all of us need to do.
As for the answers, Jesse, I don't want to be brutal, but no, you won't get the answers. None of us will. But think about this for a moment. Can you imagine asking, as you do:
how can a father fuck his own son?
and then someone comes up to you and gives you the answer? That is, can you imagine hearing an answer that makes you think, "Oh okay, now I get it", and you walk away satisfied?
What I'm getting at here is that we don't get answers because there are no answers out there, at least not the kind of answers we want and need. A therapist or researcher may be able to explain the process of thoughts that make the abuser think it's okay to do what he does, but at every step we would be shouting out that this is total crap and nonsense. And it is. Like I said, it all comes down not to real reasons that give a satisfying answer, but rather just to the abuser's "distorted thinking".
And maybe that's the good news, Jesse. There's not a single thing in the world that could possibly excuse what happened to you. All those things you talk about above? Not a single one of them leaves the slightest blame or shame on you.
I am so sorry to read all this, but at the same time I'm so proud of you for being able to talk about them. Just remember that you are talking about your father's guilt and shame, not yours.