My first impression was that you are very mature for your age - especially in terms of how you are dealing with this problem.
I want you to read through my entire answer and then decide what to do.
First I want to deal with the issue of your mother - and you will see later why. Your mother left the two of you and your anger at her is quite understandable. I can also understand that you do not want to talk to her.
Here is probably the most valuable thing you will learn in your life, and you can apply this to any situation. Whenever something bad happens, it happens because it is life teaching us something about ourselves. Your mother left you at an age where you still needed her. She left for reasons that make no sense to you. You have these strong emotions about her, which is natural.
I want you to take a step back for a moment and think about how you have changed over the past four years. Compare yourself to your friends. You sound quite mature - like a young adult, and with wisdom beyond your years. Would that have been the case if your mother had stayed with you? Probably not. You might never have thought about this, but you have gained a lot from her leaving you to grow up on your own. You have a sense of responsibility that your friends probably do not have, and I am sure if you stop and think for a moment, you would be able to come up with a list of ways in which you have gained from the absence of your mother.
Why did I tell you this? Because I feel you are dealing better with the situation than you give yourself credit for. And because I wanted to make it clear that I feel what I have said above is as much counseling as you need.
Now for your dad: You are obviously in a strong position here, and I wanted you to understand this. You could speak to your dad about what you have discovered, but it does not feel appropriate and I cannot see how that would improve the situation.
That is why I want to advise you to find a family counselor near you, and then insist that your dad goes with you. He will probably go if you tell him that you are struggling to cope and you need his support. Think about it. If you insist that he goes for counseling, he would not understand why and he may refuse. But if you ask him to go because you feel you need it and he is your family, he can hardly refuse.
Then you ensure that you see the counselor alone, and tell the counselor why you are concerned about your dad, and why you did not want to deal with it yourself. Then leave it in the hands of the counselor.
As far as I know (and I am not an expert on law) what he did is not a crime but the sooner he can get help, the sooner you will have peace of mind. Whatever is said between a client and counselor is privileged information and your dad will not go to jail because he gets help - even if he gets help when he is under the impression that he is helping you.
About your mom - just keep working on finding reasons to thank her for her actions. You may not understand it now, but every kind thought you send her way helps her to heal her own life and is an investment for the future.
I also understand that you sometimes feel intimidated by life. Can I tell you that is much healthier than most other people who just breathe and live from day to day, never thinking about their lives or their purpose? You are already leading a meaningful life and if there was nothing to intimidate you, it would not be life. Then you may as well watch soap operas all day and focus your entire conversation on those fictional people.
You are a lovely girl and you are very brave as well.