Many people exposed to ebv do not develop infectious mononucleosis, but will have mild symptoms or no illness at all. In fact, 85%-90% of adults aged 40 show evidence of ebv infection at some point by having lasting antibodies detected with a blood test. There may be a small subset of folks that don't develop lasting antibodies or may have dormant virus, but this is rare.
When we test for ebv, we test for evidence of current infection and of previous infection. You may have tested negative for current infection which is good - you shouldn't have a current infection of ebv if you have had it before. You may or may not have been tested for evidence of previous infection. You may want to speak with your doctor about what tests were done which might clear up any confusion. I hope this helps!