Im not sure that hypothesis fits. At the end she gets captured and delivered to the dude. In that scene everybody interacts with both characters. Also if I remember correctly, when they are both hugging in the support group, the therapist approach them, looks at them both “supporting” each other and nods. That scene wouldnt make sense if he was there alone just standing by himself.
Its always implied that dude did a lot of masturbation as marla was one of his other alts.
Spoiler alert for the fight club:
spoiler
Im not sure that hypothesis fits. At the end she gets captured and delivered to the dude. In that scene everybody interacts with both characters. Also if I remember correctly, when they are both hugging in the support group, the therapist approach them, looks at them both “supporting” each other and nods. That scene wouldnt make sense if he was there alone just standing by himself.