First of all, I want to congratulate you on ending the relationship. That must have been so difficult for you; but it definitely sounds like it was the right decision. You should be so proud of yourself for not only reconizing what was best for you, but for following through and actively taking steps to get there. Yay for you!!!
Have you blocked him from social media yet? It makes it so much more difficult to move forward when you see constant reminders of the person you were with. Fortunately, my ex doesn't have any social media accounts for me to creep on, but his new girlfriend (and the mother of his 11 month old son) does, and I still find myself creeping on her FB page from time to time. What you are feeling is completely normal. You thought this guy was going to be great, and you saw yourself with him, and you allowed yourself to be vulnerable with him. That's not an easy thing to do, and it's even harder to break away from someone you've shared pieces of your life with, even if it wasn't a long period of time. It's the level of energy and emotion you put into a relationship that solidifies the significance of it.
As far as your ex's behavior goes... well it's no surprise that he's trying to hurt you. It's typical behavior of people like him to do things that will make him feel better, and you feel worse. I highly recommend that you block him from social media, it's not like he will get a notification that you've done it. It will help you move forward. However, if you aren't quite ready for that yet, then continue to focus on the things you've been doing to make your life better, like your dance class and working hard on yourself and spending time with friends. Friends are there for you to lean on at times like these, and this is a time when you really need them. Be thankful for the people you do have in your life who are there for you, and who want the best for you. As for the friend of yours who showed you the texts... that is kind of a silly thing for her to have done. I am sure her intentions were honorable, but all it did was make you feel bad. Maybe tell your friends to avoid talking about him, or giving you information about what/how he is doing. The more distance you put between yourself and your ex, the better chance you have at moving forward.
Best of luck to you! We are here for you!
"Caring is not an advantage."