I have an ex-boyfriend that is going to my emplyer to tell them I committed health insurance fraud, who would persue that?

It is very unlikly that anyone would think that his word alone proved anything, particularly since you lived together and no one could possibly prove who actually took the pills. Empty bottles do not seem enough. If anyone from the insurance company calls, call a lawyer betore you talk to them.

If he tries something like that, you might report him to the cops for extortion since he obviously has some sort of ulterior motive.

First, I agree that it is unlikely that anyone is going to take an ex-boyfriend seriously simply because he is in possession of four medication bottles. Secondly, if you are questioned by anyone about the incident, answer nothing without legal counsel.
Finally, if he actually carries out his threat and contacts your employer, you may have a case against him for fraud, harassment, or false light invasion of privacy. It is all very fact dependent, of course, but if you are concerned, perhaps you should contact an attorney now, who can be in contact with him before he tries anything. A letter form an attorney can frequently make someone think twice before proceeding.