Keep yourself busy with family and friends. Bf and gfs come and go, but family and friends are your anchors. Also, try to think of the reason that you are thinking about the person in the first place.
That may help it be easier to deal with. If you are thinking about them for good reasons, then don't worry about it too much. If it is because the person is bad for you and you don't want to think about them, then think about what you really want in a person and focus on that.
The best thing to do is find a hobby that will help you take your mind off that person. Being around freinds and family are also good sources for redirecting our minds. Staying busy and having fun has been a proven factor as well.
I have found to that writting a page or two about the reasons that you are no longer with that person can also be beneficial to relaxing your mind. I found this site and it has several books and other suggestions for why our minds work they way they do. innovationwatch.com/deepchange/books/bks....
Try distracting yourself by reading a book, going shopping, watching a movie, making a craft or baking, etc. Might help for a little while.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.