No, the polygraph is how you show him you are not taking it any more. If he refuses, divorce him or live a life full of his lies.
I do not recommend your separating unless he refuses to take the test.
Trust will find out a lot more....and then you can work from a place of honesty and knowledge.
Do NOT trust him when he comes clean on a few more things after he agrees to take the test...make him take the test. He is a known liar and should be treated as though he is still lying.