I heard mono is the disease that never dies. is this true, does mono truely never leave your body? will your immune system be permanently weakened?

Not true: While mononucleosis can occasionally cause more chronic problems, the vast majority of times the bodies clears the virus and the infection resolves.

EBV: The epstein barr virus, like other herpesviruses, remains in your body for a lifetime once you have acquired it. Fortunately it seldom produces recurrences of disease but simply remains dormant in your body. Whether this in any way affects your immune system is not completely known, but if it does it is not likely for you to notice it, and you will also be sharing it with almost all other people.