Office Romance in the past

I am the assistant manager of a small organization. Before we were absorbed by a bigger company, we did not have a dating policy in place. During that time I dated one of the employees for 7 weeks. We ended it 9 months ago. Ever since, the employee has been uncooperative, hostile, circulating rumors, and at times making threats of going up to management with it. Even though I don't have control over his salary, promotions or schedule, I am the direct supervisor.
I am currently involved in a melee with my direct supervisor over unfair scheduling practices. It has escalated to HR and I am concern the affair may come up at some point to my detriment since the new company has a strong anti-dating policy. Please advice.