"[Bo] said his soul thumped inside of him and it felt like he’d known you and loved you for a thousand lifetimes."
(They sang together the first time they met, FYI, and that's the time they refer to here.)
Now Ember and Bo's love is so great that it made Ember's best friend's boyfriend want to take a break from said best friend, because he wasn't sure they had the same kind of love Ember and Bo share. The kind of love they share after knowing each other five, maybe six, days. Yes people, this is happening.