Your FPR must be faulty and letting fuel through at all times. The way it should work is this:
Engine off - no vacuum - FPR valve closed and fuel retained in the injector rail.
Engine on at idle - high vacuum - FPR valve open, some fuel returned to tank
Engine under throttle - low or no vacuum - FPR valve partially open or closed, less or no fuel returned to tank.

If you pinched off the return line and the car started up, then the FPR is open all the time and when you tried to start it before, the pump couldn't build enough pressure in the system.