Spears's estranged husband, Kevin Federline, is anxious about his wife's condition – and about the couple's two sons.
"Britney scared everyone pretty bad. Kevin is worried that's for sure," a source close to Federline tells PEOPLE. "Kevin just wants her to be OK. He loves her, so however she can get better is just what we'll have to accept. [They] will make it work with the kids – it's all still for them."
One person, who also agrees that Federline has Spears's best interests at heart is her childhood friend and first husband, Jason Alexander, whom the pop star wed in Las Vegas in 2004 (their marriage was annulled 55 hours later).
Federline is "a good dude," Alexander, 25, told PEOPLE on Tuesday, the day before Spears checked out of the Promises rehab center after a one-day stay. "I know he takes care of those kids."
Alexander, who in November called Federline "an idiot," now thinks Spears's estranged husband "just got caught up and manipulated," he says. "Maybe getting Kevin out of her life wasn't the best thing for her."