Britney Spears was reportedly lost in her own world during her relationship with Jason Trawick.
The 31-year-old pop star and her 41-year-old talent agent ex ended their engagement last week.
Jason has moved out of their shared residence and no longer acts as one of Britney's legal conservators.
It is claimed that Britney wasn't mentally grounded enough to be cognisant of the tension between them.
"He had been planning to break up with her for months," a source told Us Weekly magazine.
"Everyone knew Jason was leaving her but Britney. She's in la-la land."
Speculation is rife that Britney's milieu are concerned about her mental health.
They don't want Britney, who remains the subject of a conservatorship order following her 2007 meltdown in which she shaved her head bald, to have another mental breakdown.
"Everyone is trying their best to keep grounded, but they're scared it could happen again," a source told In Touch magazine this month.
"She was so different, strange new bangs. She just didn't seem pulled together."
The star's father Jamie is now her primary overseer.
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