Joe Manganiello is officially off the market ... he's engaged to longtime girlfriend Caitlin O'Connor , TMZ has confirmed. Sources close to the couple tell us ... the two are engaged and are excited for this next chapter in their lives. We're told, Joe announced Caitlin as his fiancée at the San Diego Film Festival during his speech last night. He thanked his betrothed for her love and support while accepting his Career Spotlight award. It's unclear when or where the proposal took place ... but