Is the questioner considered a pimp for being jealous over his paternal aunt and ordering her to be modest, despite his sexual arousal towards her and masturbating while imagining her?

Falling into the desire for one's paternal aunt is a path to destruction. One must stay away from her, lower their gaze from her, and masturbation is forbidden.

Lack of jealousy over one's family and unmarriageable kin (mahram) is a form of cuckoldry (diyāthah). The questioner might be affected by some of this due to his lack of jealousy over her from himself.

One should strive to get rid of this desire by diverting the mind from such thoughts, keeping company with righteous people, filling free time, hastening to marry, and persistently supplicating to Allah to avert evil and indecency from him.