Not exactly sure about how you explained your situation but I think you are saying the source of your "sadness" , your ex-fiancee, is gone from your life. If this were the case with a little adaptation and time you should be fine. But you should know that "depression" is not a mood it is a mental illness with many legitimate causes.
I suggest looking online at places like wikipedia to see if you fit the profile for a person with depression, then speak to a psychologist ( not psychiatrist ) to see what they think. The only quick fix that is popular with doctors for treating the blues is stuff like prozzak, but there r natural ways to elevate mood ( I suggest staying away from street drugs, cigarettes and booze...all highly addictive and of questionable quality ) ...really it has to do with your personality...feeding the birds, going for a swim, whatever makes you happy.
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.