Is sex addiction a really medical condition?

Yes and no. yes - sex addiction had same neural pathways as other addictions which are characterized/defined as "brain diseases" therefore a medical condition. No - many professionals and lay persons don't recognize sex addiction as medical but rather a moral, emotional, behavioral and/or psychological problems that can be corrected. Sex Addiction is serious condition w/devastating far-reaching consequences. .
Depends who you ask. If you are a victim, then its a crime. If you are a treating psychologist, it is a psychiatric condition. If you are a lawyer, it is a legal definition. In my opinion, it is real but rare. Just liking sex a lot, even really a lot is not enough to make the diagnosis.
Sex Addiction? Not everyone considers "sex addiction" a useful diagnosis, in the first place. Read Dr. Marty Klein's thoughtful perspective on it: Suggest consulting w/ a sex-positive therapist to understand concerns you may have about yourself (or other person) in relation to compulsive sexual behavior.