A relationship usually between man and woman where they are old and mature enough to be having sex on a regular basis, but do not. This may occur for several reasons, but it is not considered an unsuc-sex-ful relationship if they do not have sex because of health problems. An unsuc-sex-ful relationship usually turns into an unsuccessful relationship because one of the adults who wants to have sex gets tired of sex deprivation, leading to random, pointless arguments.
"What happened between you and that other girl, I thought you guys were perfect for eachother?"
"Yeah well, it was an unsuc-sex-ful relationship."