Yikes! Everybody fears rejection to some extent. My suggestion would be that instead of asking yourself "Why doesn't she want to play with me?" just ask yourself "Am I playing fair?" and "Am I having fun?" If you are playing fair and having fun then you really won't feel the need to concern yourself with anything else. Of course, there are stickier more difficult issues along the lines of "What constitutes fair play?" and "Why aren't I having any fun?" but still these are problems you can solve by and for yourself.
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver
