BJT astable multivibrator generate triangle wave
So the output of vibrator is a pulse which should be the input of the integrator as to gain the triangular waveform. In your simulation R6 =1 milliohm instead of 1 Mega. 

You are basically shorting the integrating capacitor.

The correct symbol for megaohm = Meg in LT spice.

EDIT: As Bimpelrekkie mentioned, since you have a open-loop system your op- amp will drift.

The simulation below shows how you can charge and discharge the capacitor based on the output. 



How it works ? 

So at t=0 , assumme output is zero and the output of the flip flop is zero.
The input at summing amplifier has only the negative dc voltage, this causes a linear rise due to the integrating capacitor.

Once the (arbitrary) threshold of 7V is reached the Comparator U2 goes high and sets the Flip flop which has an output voltage of 2V. 
As a result, the voltage at the output of the summing amplifier jumps from -1V to (-1V + 2V) 1V, this causes the voltage to fall linearly. 
Once the voltage goes below 0.05 V, U3 goes high which resets the flip flop and the summing point jumps back to -1 and the cycle repeats.

Do not mind the simulation is not very neat , but gives a idea how you could approach the problem.