Differentiating between SX as a subtype and Type 4 is difficult since there are many similarities. Push pull relationships are not only specific to SXs, they are also specific to 4s interpersonal experiences. SXs and Fours both like intense romantic encounters. They live for INTENSE EXPERIENCES - The more intense the better. Like 4s, sexual types are intimacy junkies - it relates to intensity and the desire to merge with the other. Fours also have a tendency towards depression - so it really doesn't help to describe SX Fours as having propensity for depression when relationships go sour... uh...yeah...that's what any Four would do - -and come to think of it...any person would do. BUT...not to the same depths as other Enneagram types. The depression runs deep. There are other SX and Four parallels.
The point is: It's really difficult to identify a Four as a Sexual Type - the descriptions overlap quite a bit. The only way to really figure it out would to be to identify the Four in question as MORE FOUR (that is, the Four is not particularily motivated towards self preservation or social activities). By default you would get SX Four.