is that why the saying goes .. "once a cheater, always a cheater"?
NO. The saying is, "ALL CHEATERS LIE -- PERIOD."
But the recidivism rate for infidelity, IF one follows a thorough plan which includes sending a no-contact letter, complete transparency, and good MC or FT with someone trained in infidelity, can be quite low -- I'd estimate less than 20%.
However, WITHOUT those things, I'd place it well north of 90%+.