Why does she need space....

Hey, so me and this girlfriend recently started dating once again (dated for a couple months last year) after a long break a little over a month ago. We became officially boyfriend and girlfriend a month before christmas break and still managed to keep in contact via text every day of the break. When we returned to school I tried hanging out with her the first week back because I hadn't seen her. She started acting differently for unknown reasons - she stopped asking to hang out as much, never asked to stay over for the night, and started making up weird excuses not to hang out. SHE was the one usually asking to hang out, and suddenly it became me. We did end up see each other one time the first week until she claimed that she needs space. This took me by surprise because I wanted to see her since I hadnt over such a long period of time. If this was when we had hung out recently a lot, I would understand, but we haven't. It's been three days and no communication has occurred. How long should I wait to contact back, if I should, and should I just end it because I dont want someone who needs space from me? Is this just a change of heart from her?

Most likely, she's banging another guy, and if not, she wants to.