I went through the exact same thing at 58 with my high school sweetheart... It took years for me to stop crying (the first year as much as three hours a day), and I never stopped thinking about him...although not always fondly. It is now five years later, and just yesterday, I felt his presence in my car for a minute or so as I was driving home from work, almost as if he were sitting next to me.
How long it will take to settle down depends on the circumstances of your life, the intensity of your feelings for him, your age, your general health and lifestyle practices and how much support you have.