Many times it does not take much for a boyfriend to leave you, possibly for ever. If you experience this heartbreaking incident do your best not to lower yourself by begging him to stay or crying your eyes out. The reason you want to be composed, as hard as it may be, is to set yourself up to be able to get your guy back later.
If at the time of the break up there is a big fight over it and much arguing, both of you will hold this anger for far too long and will not want to see the other person. If you can make the break up as peaceful as possible the chance of seeing your ex sooner than later is greatly improved.
In fact your ex may be wondering why his breaking up went so well. He may start to think that you did not care that much about him which will start to work on his ego. This alone can make him keep thinking about you and what he may have missed. Of course you are heartbroken he left you so now spend some time on yourself.
Don't worry about your ex boyfriend right now. Don't try to contact him or spy on him for 2 to 3 weeks. Use this time to get your emotions back on track so you can start to think clear again. Get out and enjoy yourself with your friends so you start to feel better.
Hopefully if the break up went the way you hoped, your ex will call you to see how you are doing, remember he should be curious as to why you did not fight about him leaving. If after a few weeks you have not heard from him, give him a call just to ask if he is doing ok. Make this a short call and act as if you are doing great. Keep the call short unless your ex wants to talk. Otherwise say you must go and politely hang up.