This is NOT a poorly written story. Sadly, it’s not a unique one. There are other kids of divorced parents who are caught in a similar bind. Thank you for sharing. It gives me a way to not only talk to you but to talk to those other kids.
Your mom’s behavior suggests to me that she is suffering and feeling very much alone. She is reaching to her kids for comfort and validation; something you are in no position to give her. She must feel like friends and relatives aren’t there for her. She therefore talks to the people who quite literally are there — in the same house.
Your image of your dad isn’t “ruined” unless you let it be. You have no idea if he really did the things your mom claims he did. You reported that your dad defended you kids when he lived with you. Has it occurred to you that just maybe she was equally critical of him to the point that he felt he had to leave? What he maybe didn’t factor in was that he was leaving you kids to deal with something every day that he couldn’t deal with himself.
One of the good parts about getting older is that we see things from a different perspective. You are now entering your teens. You are asking good questions. You are less dependent on your mother to provide you with answers or information. And you can think critically about things she says to you.
It’s sad that she is so deep in her own pain that she can’t be a good friend to you. But the good news is that there are probably other women in your life who would be glad to take on a closer role with you. Think about relatives like a grandmother or aunt who might enjoy spending time with you. No relatives? Some kids get close to the mother or relative of a good friend. Others get close to a teacher or guidance counselor or coach. My point is — stay open to letting in possibilities for finding an adult woman mentor and friend. For now, step back from expecting it of your mom. For reasons you don’t yet understand, she simply can’t do it.
As for your dad: Since you don’t report any abuse by him, why not spend time with him and get to know him for yourself? At some point, it may feel appropriate for you to ask him his side of things. But I wouldn’t start there. Build some relationship first.
As for your friends: I don’t think they don’t care. They probably don’t know how to respond to your situation and feel anxious about doing or saying the wrong thing. So they steer the conversation to topics that are more comfortable. Focus on being a good friend to your friends and eventually someone will become close enough to you to become more of a confidante.
I wish you well..