Family pain

So I am a mom to a young boy. When he was 3 he was molested by my 12 yo nephew. My son came to me and told me what happened which stopped me in my tracks and broke me. My nephew and I used to be super close and now I can't even stand to think of him at all. I'm disgusted and since then I've completely disowned him. My family didn't believe that he did it at first which honestly really hurt because it felt as though they took his side over my sons who was the victim and I've been struggling with that ever since ( it's been four years). My son has been bed wetting ever since- he had stopped prior to it happening. Now, apparently my nephew did it again and was taken out of my sisters custody ( she is not the best mother) and my mom took him in. Is it wrong of me to feel hurt that my mom took him in? On the one hand I understand he is also her grandson but on the other she knew that meant she wouldn't be able to see my son. I am just so sad all of the time and feel like I failed my son every day because this happened to him. My depression was so bad that I had to move to a different state to get away from it all and try to start fresh with my family.