I'm sorry you have had personal issues in your life stemming from your wife dealing with sexual harassment issues from the HR side, but your emotional reaction based on that experience isn't likely to be the basis for sound advice.
> If two employes can't resolve their own issues without involving you then you don't need them.
No employee should be subject to harassment. And as a consequence of being harassed they should not be cast aside. Part of being a boss is dealing with these situations. Even if dealing with it means handing it off to a lawyer and HR to resolve for you because you don't have the time or expertise.
> If the innocent party was truly free of blame you can always hire them back.
I can't get my ex back. Firing someone burns bridges.
Once a startup goes beyond some friends/colleagues tinkering in their garage or bedrooms, you need to retain proper staff to handle your various employee situations. You need people that know how insurance works. You need people that understand retirement plans. You need people that understand legal obligations re overtime, travel compensation, etc.
With a small company you can conceivably get away with a handful of lawyers on retainer, or one primary in-house counsel who consults with specialists as needed. But you can't get away without having lawyers and HR people in the long run.