The "Umbrella" singer started dating Chris in 2007 and friends claim she is so in love she doesn't like being parted from him.
A source told America's OK! magazine: "She has to have Chris around her 24/7. If Chris is with her on a photo shoot and steps away for a second, she starts saying, 'Where did he go?'"
"If Chris isn't with her, she wants to call and check in every second. She's crazy about him. Rihanna constantly talks about Chris."
The 20-year-old singer – who prompted rumors she was engaged to Chris, 19, last month when she was spotted wearing a giant diamond ring – has previously admitted she finds being on her own difficult.
She said: "My biggest challenge is being away from my family and friends, and all the people I love and I'm used to being around. It's hard for me to just throw that all away and be by myself."
During Chris' recent London concerts it was reported Rihanna banned a host of beautiful female stars from meeting him backstage.
