I get sad when I find out a girl has deleted me
It's quite normal for a girl to delete someone that she is not interested in communicating with.  Why does that make you sad?
Girls give me great pleasure and fun, I am unmarried and I am still young.
The internet can be a pretty impersonal place, but you shouldn't take it personally if girls decided to delete you. You probably deleted a lot of girls that you didn't find attractive so why worry when it's the other way around?
I will try to not care so much.
That's probably a good idea.  If a girl was willing to delete you without a word, then she probably wouldn't have been worth spending time on, since that wouldn't have gotten you anywhere.  Just concentrate on finding people who are interested, and forget about the ones who aren't