Honestly I'm not mad at his choice, but it sounds like their relationship wasn't that serious. Which is comprehensible since it's only been 6 months.
But me if I really like her, I'd help her out for a set period of time. Not letting her ass out. Like she moves in, pays what she reasonably can, and once the month ends we assess the situation.
Would be like a trial period. If I see she's really working to get her independence back and easy to live with, then we can extend. If I see she's getting comfortable too quick, she'd have to go at the end of established period.