Well, you told him to take his stuff and get out.
You told your 11 year old son to move out of your house. In a strop.
Hardly father of the year material, is it? Whatever happened to sitting down with a pizza for a chat and trying to talk through why his friends don't like you/ whether you could arrange for him to bring a friend camping for the weekend/ you'd go and ride bikes with them in the park... Or even explaining that you love him very much and would like to spend more time with him, but that you understood he was getting older and it was perfectly natural that he would want to spend time with his friends and not his parents?
Being reassuring and a parent?
Instead of tantrum ing and throwing him out like a sulky lover?
Yep, I think your ex is bang on. Time to act like a parent and start trying to build bridges with your child, who incidentally is growing up. You wouldn't want to be teaching him the wrong thing about how to handle this sort of confrontation, or making him feel bad for going through a perfectly normal stage with approaching adolescence, now would you?
You obviously started well, with trying to find out why, but then the criticism got a bit personal and you threw your toys out of the pram instead of discussing what you could to help the issue.
Go apologise, and reassure your ex and your son that you won't ever turn your back on him again.