I would simplify the circuit quite a bit, design the 25nn as though it didn't have current feedback, and just use the standard 2 resistors for voltage feedback, then design a current amplifier using the sense resistor your using, and connect the o/p of this to the feedback pin on the 25nn through a 1n4148 diode, so that when the current reaches the set point the op amp lifts the feedback voltage up against the 2 resistors and causes the chip to wind back on power a bit, if you use a slowish op amp like a lf358 you might get away without compensation, you dont need rail-rail as the '358 goes to ground and the feedback voltage is only 1.25v, make sure your grounds a
Also 1m feedback resistors on a power circuit although it might work are not advisable, the system will be sensitive to noise and possibly supply ripple.