people who frequently accuse partners of being unfaithful without evidence are generally those who are cheating themselves or have cheated in the past.

I would guess that people who were cheated upon by their former partners also have increased the prior probability of someone cheating on them.

That's generally the problem with this type of reasoning. A strategy used to find a perpetrator by exploring familiarity with the crime, may also find a victim. If you overestimate the probability of people stealing, you may be a thief... or a victim of theft.