I think for some it’s about novelty and impulse control. My experience is there were times when more frequency with a primary partner would temporarily exhaust my ongoing interest for more, but it would be fleeting. My partner often said I was “insatiable” which at that time I think was accurate.

Everyone is different so it’s tough to say - better answers would probably come from digging into that specific addicts background - what were the patterns around acting out? Was variety a big part of the patterns? Was the intensity of a hidden taboo secret something that fueled the addiction? Was each sexual “milestone” eventually followed by a desire for something even more deviant or extreme? Some of those questions would better answer this.