Im broken

Idk why I really just need to vent and I honestly don't have no one, So here I am. A little backstory, me and my children's father have joint civil agreement I have them one week and he has them the next, during school it's every 2 but they're being homeschooled, My daughter is almost 10 and my son is 8. So the kids are home with me this week and a few hrs ago My mom, the kids and I were at the store when the kids father called and he sternly asked to speak to my son. (I hear a male voice saying cuss words loudly in the background.) Before handing my son the phone I ask if everything was okay and he said he would talk to me about it after he spoke to our son. (His voice immediately when answered sounded angry.) I didn't know if my son had done something over there he wasn't supposed to and his dad was just gonna run it by him, Well he did do something he wasn't supposed to but nothing I ever expected. I just hear not only my son's father but the other male voice in the background yelling and attacking my 8 year old son, and my son's face looked helpless. He would never talk back to dad unless he was told to. So I take the phone and tell my mom I'm stepping out of the store and ask what the hell is going on, The male who I find out is my children's father's best friend and neighbor, He proceeds to tell me that my son taught his daughter a new "game" called Mommy and Daddy and that my son sexually molested his 7 year old daughter. Okay besides the feeling of complete shock and feeling confused and heart broken I immediately felt sorrow for this father as well, I still do and I will continue. After asking exactly what happened, The story was they (the girls family and my kids father.) decided to let my son and his daughter have a sleepover and my son taught her to play Mommy and Daddy and he proceeded to pull her pants down and touch her private part and then she kissed his cheek. I want to mention again that I totally understand her father has every single right to be upset for what happened, But I have this other feeling in me that wants to protect my son and defend him but at the same time expressing to him how wrong it is to do these things, The anger in both of their voices made me feel sad for my son, but I also have thought of the little girl and I'm just so sad for all of this. I'm upset and I am full of guilt, I have been pacing my house all day. As soon as I walked in the house I contacted a local psychiatrist and conseling center and made my son an appointment. My son's father called me and asked me what form of punishment I had planned for my son, and every thing else he said really upset me but I have no idea if I should be feeling these ways. My son did something wrong and I 100% agree and feel deeply for the girl and her family. I want my son to know the severity of the situation with him fully understanding at 8 years old. I do not feel like my son exactly needs to be punished as much as I feel he needs help and something is wrong. His father has a 2 year old daughter in his current relationship and let me know on the phone he better never find out my son touched her. He said it like our son was a stranger and they're viewing him as a man. I would like to also add my son witnessed his sitter (my 10 year old) be sexually touched by one of their dads gf male friends, and we just went through hell and back with that situation because their father chose to believe his gf and not believe our daughter and due to lack of evidence every charge was dropped after the local PD head Investigator tried really hard to rule in our favor the final decision was left to the prosecutor who called me and blew my mind by saying literally since my daughter didn't mention the male having an erection they couldn't prove just by my son and daughters story that he was touching her with sexual intent, when my daughter told me this man rubbed her boobs and didn't stop for several minutes and kept scooting close to her I never doubted her and I don't know how he ever did. We just got back to them seeing their dad regularly and things being somewhat normal after I made sure the man legally could never go near their home while she's there or her in general. I believe in my heart their dad loves them and they love him but I can't imagine why in these situations he loses compassion for his own children. I don't know if I'm making any sense or if I'm just rambling on, but I want to hug my son and I want him to know that he is not a monster or bad person but he made a bad choice and what he did is unacceptable and should never be done. I don't know if what he seen happen to his sister is somehow connected because he has never been exposed to something like that. He knows better and he knows right from wrong, Why do I feel defensive and guilty and so just terrible ladies .. my heart is broken for this little girl and her family and I feel sorrow for them, But every time I look at my child I want to break down and hold him and cry. He has been really stressed since talking to his dad. Why do I feel this way? I'm full of anxiety and stress and I just hope I'm making sense.

I also want to add I have no idea why my son was sleeping over with a girl when my kids father's girlfriend has 2 girls, the same age. I find the situation a little weird, and I wonder where the supervision was as well.