What do I need to tell my fiance about my future health? I have mononucleosis.

Have now? or had? Common viral infection. About 80% adults in us have past history mono:caused by 1 of 2 viruses: epstein-barr and cytomegalovirus. Active infection: contagious, don't swap spit. Past history: over and done. Acute infection: fatigue, sore throat, swollen glands, maybe tonsillitis, hepatitis, big spleen, anemia; usually over in 2 weeks, recovery can last 6 months. No spec rx gen; rest, no alcoho.
The truth. Mono is a generally a self limited illness that may be spread through oral secretions. It is not likely to have any long term consequences.