I have a cold sore and how long does the virus reside on my pillowcases and sheets once i get out of bed and how often should i wash the bedding?

Good question!: The only issue is spreading to someone else. The virus does not live very long off the human body (out of the cold sore). It is contagious with direct contact mostly by touching or kissing. That said, you don't want to share pillows with someone else when you have one. I don't think the virus lives long enough to be active the next night when you sleep.

Not long: Herpes virus lives a very short time on dry surfaces, especially sheets. The risk of transmission via sheets is exceedingly low. The virus sheds in body fluids (saliva) so as long as your pillow isn't saturated you should be fine. Cleaning frequency is up to you :).