People often mention “long-term relationships,” but generally speaking, how long do they have in mind?

Also, do relationships that begin through a dating club—perhaps considered impure by society—really tend to last as long as people hope? I often read the dating blogs of men who seem to be members of Universe as a reference, but they don’t really give off a “long-term” impression. He seems to be quite an experienced dater, but is it still difficult even for someone like him? Or is the hidden reality that dating clubs simply aren’t really suited to long-term relationships in the first place?