You have been in the relationship for 10 years. That is a lengthy period of time you've had the relationship with your ex. You were happily looking forward to when you would get married to your ex. But, out of the blue, he ends the relationship. He says that you're better off married to another man.
This doesn't make you bad. You're not bad. It might be there were some things in the relationship that might have led your ex to break up with you. However, no one is perfect. Even your ex is to be blamed for the demise of the relationship.
In fact, your ex is the one accountable for the breakup and hurting you. Why did he wait all those years to end the relationship when you strongly emotionally bonded to him?
Don't blame yourself. Don't blame your ex. Admit the relationship is over. If there are things in your life that need to be changed, it's better you do so.
Remember, a person isn't bad because of their weaknesses. A person is bad if they don't change their negative behaviours/attitudes. A person is bad if they are unfaithful, lack respect and doesn't care. The person doesn't want to change or admit they are wrong.
You have stayed in the relationship for long and were looking forward to getting married. This doesn't make you bad. It has made you a victim.
What to do? Don't contact your ex. It's time to allow the healing process to begin. It's time to move on. You have to move on.