Blatantly honest post. It takes courage to state your vulnerabilities openly.
The mind plays many tricks with us, especially when we try to focus on something difficult. I suffer from the same traps of irregularity as you.
During such times, I focus on momentum. I take tiny steps, but try my best to stay consistent with them. I set weekly targets (not five-yearly ones) and check my progress. When I falter (today is one such day), I mull over how I can get back on track quickly.
The answer to your last question decides how fulfilled we feel each day.