I'm not sure how much sexual addiction there is in relationships.
More often than not during the initial "infatuation phase" of a new relationship sex is at it's most adventurous & highest frequency.
Once you get beyond that period and there is an "emotional investment" or there has been a few major disagreements both people tend to revert back to (their normal libido) levels. If it turns out one person wants to have sex 3-4 times per week and the other one is content having it once a week or every other week that can lead to problems. Generally speaking the person who wants more sex is "shamed" into accepting less sex or they decide to cheat or leave the relationship.
Addiction usually means a person ignores their daily responsibilities and obligations in order to get their (fix or high) from the activity they enjoy.
Unless one is skipping work, not paying their bills, shutting out friends and family, obsessed from sunup to sundown with thoughts and plans for finding ways to get their next whatever it is then they may have an addiction!
Just because one person has a higher sexual libido than their mate does not mean he or she is "addicted" to sex.