Sources close to the new couple tell us ... Julia and Charlie believe there are surefire ways to avoid contracting the virus -- anti-viral meds and, of course, protection. Charlie has said his HIV levels are "undetectable" and Julie says that gives her even more reassurance.

We're told Julia is hurt that many of her friends are warning her to stay clear of Charlie because of HIV, and she thinks they're ignorant and living in the fearful past. She also thinks it's a terrible message to send to people with HIV.

As for Charlie's substance abuse issues, we're told Julia believes Charlie ... that he's been clear for nearly a year and his lifestyle has become militant healthy. She believes he's clean, because he's participating in an HIV drug trial and that includes regular drug tests.