Firstly, I have difficulties to see a real circuit behind the schematic:
What's the OP buffering the PWM output, is it a power OP, can it drive a motor or at least a relays coil?
You're driving the relays coil with the PWM wave, is it expected to switch at PWM speed? Is it a mechanical relays?
Secondly I'm unable to read a sense into the 0.5 V voltage source thing.
To start with a basic motor PWM topology, I would choose either a half bridge (unipolar, two quadrant motor operation) or H-bridge (bipolar, four quadrant operation).