What is this fluid that is discharged after looking at lustful things, and does it necessitate ghusl for janabah?

One must lower their gaze from that which is forbidden to look upon. The viscous fluid that exits after looking at and thinking about that which incites lust is, most likely, pre-seminal fluid (madhy). This is a thin, white fluid that exits upon pleasure or contemplation. Pre-seminal fluid (madhy) necessitates ablution (wudu') but not a ritual bath (ghusl). It is impure (najis) and must be washed from the body and clothing.