Should I tell my boyfriend that my cancer might be back?

I’ve been a cancer survivor for almost 14 years but I’ve been having some trouble lately and I found out today that I may have a recurrence of cancer in my blood/bone marrow (Leukemia). I won’t find out the results of the tests for a while, but it’s really worrying me. I am going to my boyfriend’s house tonight and I know he’s going to ask me what’s wrong. Should I tell him, or will it freak him out? He is aware of my history, but we’ve only been dating a few months… I’m afraid he’ll leave, you know? I’m 18, if that helps any.