Obsessive thoughts are very common. Lots and I means lots of people suffer from them. You need to get clarity. get distance from your thoughts and your emotions. Get distance from this heartbreaking event. You need to gradually phase this guy from your memory and replace him with more positive experiences. Don’t be in a hurry to get into another relationship. I’d get into things like yoga and meditation, even Buddhism. Study the mind, would be my advice. Think about your values, your integrity. What kind of person do you want to become? What kind of friends do you want to have? Do you value power and money? If not, seek alternative careers/lifestyles.
Just my take on things. Good luck.