You didn't do anything wrong here - you thought the best of your father and disbelieved accusations levelled at him, which is what a lot of people would do in that situation. You were deceived and you feel understandably hurt, as well as alienated from the rest of your family. None of that is your fault. Now that you know the truth, maybe try talking to close family members about the situation and how you feel to see if you can find support there.
It might be worth looking for a support group - online or something local - for people in your situation. As I don't know exactly what the situation is I can't offer any specific links here but there are support groups for most things and being surrounded by people (even in the virtual world) who can relate to what you're going through in a non-judgmental context would probably really help.
You may also want to consider some sort of talk therapy to help you work through how you're feeling at the moment. Maybe you could ask your GP for a referral so you can talk to someone who is qualified to help you help yourself.
Remembering that you were lied to to keep you safe and sound sometimes helps. My father lies about tons of things. He thinks that saying these things will keep me safe, as if the truth is some kind of monster that might harm you. Not that it is, and more often that not, lying makes things worse.
But it's like the case about the neighbour's dog and the man's daughter (Whereas the dog, a ferocious looking pup is overtop the man's daughter and she's screaming. He throws the dog off of her and he lands in the pool and dies. Turns out he was only licking her face, not eating her.) What do you judge? The intention or the action?
Get professional help. ASAP. Im not saying this make you feel like you're crazy or like your problems don't matter...they do. You obviously need help and a bunch of faceless people on the internet (especially on a website that's soul purpose is NOT this whatsoever) is not going to help. Im not going to even give you advice on what to do except for this because I have no idea what you're going through...no on here does or is capable of helping you. Stop reading these comments...at least the ones after mine, forget you posted ANYTHING about this at all online, and go seek a therapist or someone who is at least an unbiased listener who you feel comfortable enough to express ALL the details with and thus be able to fully help you cope. Im sorry if this seemed to blunt or came off as rude. SOmetimes you need a good hypothetical slap in the face.
Here is some truth - people lie, people hide the truth maybe to make someone feel better and not be bitter. I think what you haven't done is just simply ask the person directly that you have concerns about- your father. But if you find out it was all a lie, don't take it out on your dad or yell at him. He and the others probably did it to spare you pain and all.
This is a very tough situation, but I will advice you to talk it over, be it a very close friend or your family members, who you now realize were saying the truth all this while. Holding on to emotions is not good for anyone, so try to lighten up.
So your fault is being too trusting, I could think of worse things. Your family will forgive you in time, they always do, you'll have to try to forgive yourself for whatever you may have done to them and apologize. I'm sure if you had more information you would have handled it differently but you didn't, you can't expect to be responsible for that and it's unreasonable for anybody to expect more of you.