Should you disclose? you should.
However, I can understand the non-disclosure. I don’t think it will look as bad as it is made out to be because this type of questions was not asked on the form. However, failure to answer this question might raise a “flag” as it would be deemed that the information could be used to blackmail or coerce you.
If you are truly concerned, I would advise you to consult a security clearance attorney. Honestly, I don’t see the harm in the disclosure, but then again… I am not you.