Student Exchange Programs

she was and exchange student and she came here for 1 week, the day we saw each other at school (i was helping them out) we immediatly started talking and done heeeaps of things togeather that week, when she left it was the saddest iv been in awhile anyways, my mum and dad said i would forget her in 1 or 2 weeks but its been 7 months and i still tihnk about her everyday, and its stuffing my life up now cause she started dating just the other day. but my question is, how do you get over a girl if you cant stop thinking about her?