I thought your post was going to be about a small son telling porkies.
This is a grown man who lies persistently and elaborately as an automatic alternative to telling you the truth, even when you sound reasonable and supportive.
I don't think anything you can say or do will change this. Maybe some in depth therapy but he would need to accept the problem first, surely, or he will just lie to the therapist.
If you're really keen to stay, maybe you could keep a record of his lies: date, incident, lay out the string of lies, the eventual truth, how long it took you to get there, the outcome. Present him with this, make clear you can't live with this level of deception and time wasting, getting to the bottom of issues that affect your life, finances, household too, and give him the opportunity to explain himself and engage with a way to stop. No excuses about the actual incidents, which will doubtless not be his fault, but why there is this evidenced pattern of dishonesty.
You mention you have a good memory so can stay on top of this, which must be exhausting and make you doubt yourself. What if you start suffering memory loss in later years, and he doesn't? He will make your life absolute hell. You won't know if you're coming or going. I would be bearing that in mind.