My boyfriend has some small rash like bumps on his upper lip and he says it's not painful but it's numb. is it a cold sore ? it appeared yesterday

Hmmm,...: From your description, it certainly may be a cold sore, but diagnosing medical issues, especially rashes , over the computer is impossible. If it persists, and you are concerned, have him see a Dr. for the official diagnosis, best wishes.

Sounds like: the very early beginning of a herpes labialis outbreak. These are contagious viral blisters.