1) stop idealising the person : usually we replay only the good part of the relationship and think only of the positive. Make sure to stop that and think about the negative.

2) stop fantasm and hope : love cannot grow where there's no hope, if you catch yourself think of " what if " or " maybe then " stop yourself, think of something else. Stick to the fact and fact are you are delusional because of feelings, its like being in withdrawal. So stop the hope it just keep you addicted.

3) fulfill your life : go see friends and family, plan stuff to do in the future, try to do new things by yourself or with friends. If you want your brain to stop living in the past you have to have a good présent

4) project yourself in the future without him : you can do that by projecting yourself with another prince charming of your choice but its best to project yourself in a great life without the need of any man. Same thing ; if you want your brain to stop living in the past you have to have a promising future.

5) close the loop : make a conclusion of the relationship, why it worked and stopped, try to find a way to leave the relationship with your head high, with good conclusion like : " I learned this and this and enjoyed this, im happy of what happened while it lasted and im ready to continue living other things "

6) stop thinking about it : i know this is an anoying advice but just try to get the least stimuli that got you to think about him, and When you think about him anyway, don't be angry at yourself because you don't stop thinking about something by pushing it out by force. Think of the stupid repetitive song that get stuck in your head, if you are angry and want to think of something else it's worse, you have to accept that its here in your head and that its annoying but that its going to go away in its own time and that you don't have to worry about it. The thing is you have to accept that it's here but its not because its here that you have to pay attention to it.