Don't be too hard on him - remember, you've got loads more life experience than him! No doubt the way you handle a situation now is a world away from the way you would have done it as a teenager.
You should, I think, point out how hurtful his messages have been (and could in some way have contributed to the 'jumping') and hopefully he will learn. Maybe stop him from using your phone for a while (although they will find a way!)
My experience of teenagers by the way (as I have no kids of my own) is my nephew. His mum (my vile sister) left him when he was a baby. His dad (my fabulous brother in law) unfortunately died a few years later. Nephew went to live with grandparents (my mum and dad) but looked to me for real life stuff! As you can imagine, there were problems, but he's a 20 year old joy now! Chin up, and don't get upset!