How do I get an employee's partner to stop getting involved in company business matters?

This is another one of those awkward people situations I have a hard time with.

I have an employee who reports to me, and whom I mentor, who’s partner is overbearing and inappropriate. I adore her, but I can’t take his interference anymore. When we go out for work functions or happy hours, he always attends, and talks very specific company business with us. He’s talked to me about her salary, stock and annual reviews. I shut him down and tell him it’s inappropriate for him to bring it up or discuss it with me, but he continues. He voices his opinion on people in our company that he doesn’t even work with. I’ve explained to her that there have to be firm boundaries in our relationship, and that I absolutely cannot discuss her performance and pay with him, and she’s spoken to him. It even came up in her annual review. Still, he brings up company business- coming at it from a different angle.

I finally drew the line and requested that she not bring him to social/work events if he can’t recognize when he’s crossing the line. He apologizes and attends, but can’t control himself.

I now make efforts to see her outside of work functions and request that it only be the two of us. In some cases, he shows up at the beginning or end of the outing, and corners me.

How would you handle this? What exactly would you say to her and her boyfriend? I don’t want to ruin our work relationship or personal relationship since it’s really important to me, but this guy is way over the top.