Wow, you way overstepped his boundaries and broke his trust. Why would you tell his mother all those things, if it wasn’t you asking for help, and she’s not even around to help him? If I was him, I would feel violated that you did that.
Take a break from him. He needs a break from you. Just because you feel like knowing how he is doing, but don’t want to be friends…just take some steps back. Focus on yourself and your own life right now. Let him be. He’ll reach out if he needs you.
But also, wow…you really shouldn’t be sharing personal information about people to anyone unless you actually think they’re a danger to themselves, in which case, call 911.
Honestly, I think you kind of enjoy the drama and probably wanted to talk about his feelings a lot, which can just be even more overwhelming and emotionally exhausting when you’re depressed. Do you have a savior complex? Check your motivation.
You need to take a hard step back here. You are his ex-girlfriend. Not his wife. Not his mother. You do not get to appoint yourself his caretaker and share personal information with his (problematic) family.
Reading your update, it seems more and more likely that he was just done with the relationship, and blaming it on depression was a way to end it without being the bad guy.
Really, just stop. Find something else to do with your time. If the relationship wasn’t 100% done before you sent that letter, it is now.