Bo went to Victor and told him that if Vivian didn't lay off of Carly that he would have to 'take care of Vivian' himself. Meaning he would kill her. Victor didn't want to see Bo getting himself into trouble, especially over the likes of Carly, so he made Vivian a proposition. He would marry her as she had been wishing would happen for years, however, she had to back off from Carly and Melanie.
After they got married, she tried using Chloe to kill Carly so that she couldn't be linked back to it, but it backfired as Chloe chickened out at the last minute.