The 32-year-old pop star allegedly thinks that Lucado, whom she started dating soon after splitting from her ex-fiance and former manager Jason Trawick, is not mature enough for her, reported Contactmusic.
"Britney has been have doubts since before Christmas. She really fell for David at the start of the romance, but now she feels she jumped into things too quickly after splitting from Jason. She was so desperate to have someone by her side," a source said.
"Britney's worried he's not mature enough for her - she's used to being spoiled by her boyfriends but, with David, she's been joking to friends that he's like a third son," the source added.