Did NJT abandon service on a line west of the NEC?

Somewhere recently I saw an old NJT map that included a line roughly parallel to the Northeast Corridor, just to the west (maybe through the Flemington area?). I can't locate the map right now, and I was wondering, what's the story behind this? Did NJT actually abandon a route in the 1980's? If so, how much ridership was there, and how is it that the customers were left high and dry one day?

You may be thinking of the West Trenton Line, the former Reading line. I know that NJT ran two trains a day from Newark to Reading terminal in Philly back when. It ran along the Raritan Valley Line (former CNJ), then entered the former Reading line. The train was usually two RDC 1's. I know that if I was at the Westfield station when that train came by I would be on time for my first period class. If that train passed before I reached the train station I would be late for English.

I believe these trains were the Wall Streeter and the Crusader in homage to their Reading heritage.

Take a look at this map from 1980. Lots of service on there that was abandoned/cut back.

That former line you mention is the old Reading RR New York Branch (currently CSX Trenton Subdivision). Until 1981, two trains ran from Reading Terminal to Newark NJ. These trains were operated by Conrail under support of SEPTA and NJT (NJDOT). After funding was cut, the trains were cancelled. However, NJT briefly ran West Trenton-Newark service to connect with SEPTA service from Philly, but ridership was light and so the service was cut.

Currently there is proposal to restore service on that portion due to the burgeoning development along the line.

you might interested in njt's project page for the restoration of this service. Notice that this is one of the few projects that survived the may cleanup.