She probably doesn't want to give you the wrong impression.
She is being polite, but not encouraging you to think that you will get back together.
It is good for you ~ to be able to interact with her like this; no ties, just occasionally saying a polite hello.
Do try to find things to do, to take your mind off unattainable girls. You are good with computer graphics, etc. Get more involved with that ~ with friends who are equally interested.
If you just get on with your life, then you are more likely to find your Miss Right.