The pop star's whirlwind romance and surprise proposal had a 'deep impact' on the singer, a new PEOPLE report claims.
'Selena can be a delicate flower, especially because she has had constant medical struggles, but Justin's engagement and quick marriage threw her off guard and hit her hard,' a source revealed.
Selena is currently seeking treatment at an East Coast psychiatric facility receiving dialectical behavior therapy after suffering an emotional breakdown.
'She and Justin have been on and off for years, although they were so young when it all began,' an insider told the website.
'Justin was her first big love, and she isn't over him.'
Selena and Justin last rekindled their romance about a year ago before splitting up in March.
Justin meanwhile is finding it difficult after learning about Selena's struggles.