How to break this multistage feedback amplifier to find loop gain Aβ ? (I'm using pspice)
For measuring, calculating or simulating the loopgain there are three important considerations:

(It is assumed that the loop is opened at CF for injecting the test signal)


The signal source Vs must be set to zero;
The opening must not disturb the normal operational DC bias point 
(in your circuit, this is not a problem because of CF)
The opening must not change (too much) the loading at the break point. 
(In your case, it is required that the output resistance at the emitter of Q2 is much smaller than the input resistance at the most right node of RF). Otherwise, the load impedance must be recreated.


Comment: In your circuit diagram you have shown i(out) and i(in). I suppose you know that these two currents have nothing to do with loop gain. Loop gain is measured as a ratio of voltages at the breakpoint.