There is no harm in merely loading a nonsecure website, but you should not use it to divulge any personal information such as an email address.
Similarly, the mere disclosure of an email address is not in itself harmful. If you should receive a harassing email dispose of it as you would any piece of junk mail.
If that communication were to breach the threshold of criminal activity such as blackmail, then treat it as such. You might want to consult an attorney / law enforcement etc. That goes beyond any technological solution.
Apple provides the following information: If you see a 'Not Secure'' warning while browsing with Safari - Apple Support
Excerpt:
- The website is unencrypted and asking you to enter password or credit card information.
Example of an unencrypted website:

If you attempt to tap or click an element in that page to "sign in" or otherwise provide some information, that warning becomes more prominent. But you can just as easily provide personal information to a website that is completely secure, and it won't show any warning. The information you provide could still be used in an attempt to harass or defraud you in the exact same manner.