Sebastian didn't say much after reading the letter.
He wanted to send Jen a message but he was not sure if she had blocked him on the apps- if he didn't send her any messages, he would never know.
He was terrified of seeing the red mark of not being able to send anything to her, so he chose to give her some time- and also give himself more chances to win her back in time.
Luna seemed more upset than Sebastian with the letter and its lack of useful information- Jen never contacted the two of them when after she arrived at her mysterious destination:
"Maybe next week, she will be back already!" Luna comforted Sebastian and herself.
But he knew it wouldn't be that soon- knowing Jen, she would only be back if she had gained back her life.
Jen didn't know where she wanted to go- she never knew that it was an option for her to run away but Papa Ross sent her a message when she was crying in Jackson's room without a clue of what to do next.