hi there, i have read about ur problem and i must say it is difficult ...yet possible. First and formost stop fighting urself about not to think about him (or them). It would be unnatural if u could do that. If anything happens such as this it has happened becos we wish to take that risk as we really really want it to happen. So there is no point regretting anything now. If u r a person who takes things as they come then this is the exact time when u gotta stand up for ur ownself as noone else will do dat for u. He was and still is very much part of ur life becos this always was the deal from the begining i.e.  u cant choose whom u ll love and same way when they want leave u dont have the control over them as well. Its like those things where u dont have any control over right now. Fighting these thoughts is only gonna fatigue u more. The moment u stop fighting these thoughts u ll realize that its not ur loss but his. so pull ur self up and take this as a chance to prove it to urself that u r not defined by someone else but ur own self. Hope this helps u but still feel free to consult again anytime. thank you.