Children and parenting

I feel like a complete shit parent. I’m a single mom and have been raining 4 kids by myself for about 9 yrs. My kids range from 15-7. I’ve been having major problems with one of my kids to the point where he hurts other family members. I’ve tried everything. I mean EVERYTHING to stop the bad behavior. From time out, spanking, extra attention and he still does don listen. When in trouble or hurts his little sibling he laughs and finds it funny. When I take something away from him he screams, fights, kicks and calls names. I can’t handle it as my emotional and physical strength is just not there anymore. I felt the only way to get things in order is to drop him off with his father since he hasn’t been around to see the behavior. He makes me feel like the lowest scum on the planet not realizing I’ve tried to fix our son’s problems to no help in changing. He’s been to therapy also. His father is now wanting to keep our son and enroll him in the district they are in. Is it THAT wrong of me to be ok with it so the rest of my kids are out of my son’s harm. He’s still MY son and I feel like it’s all my fault but I also feel like his dad needs to help as I can’t seem to get him under control. He’s 10 btw! I’m very upset about this and do not know what to do… I have been extremely upset about this and crying constantly bc it’s my son… Please be nice🥺