While Spears had occasionally left the facility during her stay, including stepping out to get frozen yogurt and going to a hair salon, her departure on Thursday comes as her treatment has now ended.
The singer's longtime boyfriend, Sam Asghari, picked Spears up at the facility, and ET has learned that he has given Spears unwavering support throughout her road to recovery.
"Sam has truly been there for Britney," a source told ET on Thursday morning. "He encouraged her to get the help that she needs. He's supported her through the difficult decision to check into a facility, and he's been there to support her throughout."
ET learned earlier this month that Spears had checked herself into a health facility. A source told ET at the time that she made the decision in order to deal with the tremendous stress she's been having over her father, Jamie Spears', current health crisis.
The check-in came just a few weeks after she put her career on an indefinite hiatus, postponing her album and putting her Britney: Domination show at Park Theater at the Park MGM resort in Las Vegas on hold before it even began.
For more on her time in treatment, watch the video below.