Alice y Jack

Watching the first episode, it didn't feel like the first one it was like I was missing an episode. I don't understand where and when they became obsessed with each other they just seemed miserable, it was an average meet up with not much chemistry then all of a sudden he's pining over her and they are back and forth over and over, but why ? I'm still halfway through the series but does it get better? Was hoping for a better series to be honest especially with the actors involved. It doesn't feel like years are passing by either, both of them look no different during the time jumps lol should be better.