As for how the teen is doing? The source says she's hurting but had to do what she had to do.
"She is upset and sad but feels like she had no choice and she couldn't stand for being cheated on and being in such a toxic relationship," added the source.
The source added that Kourtney Kardashian's ex was "unfazed by her decision" and "doesn't seem to care too much." The insider says that she fears the father of three, who has struggled with substance abuse issues in his past, will "spiral out of control immediately without Sofia around."
Despite, the fear and worries, she feels "like it can't be her problem right now. He took her for granted and she can see that."
The insider also says that Sofia is leaning on her family to get her through the tough times, staying at her dad's house while she looks for her own place.
"She is relying on her family for support and they are trying to keep her busy. She is spending her time with them and with her close friends," said the insider.
Just seven days ago, the teen posted a sweet photo of the duo on Instagram and wrote, "Happy birthday Baby! Thank you for being you. Love you."
Prior to the split, things had been going well for the twosome. Just last week, a source told E! News Sofia and Scott were "talking about moving in together permanently."