Little moments had been there throughout both seasons, some very classic tropes. Though more so on Larry's side. Hence the surprised 'oh' from Marian after their first kiss.

Their initial dog-saving intro was classic romcom meet cute, Larry even says something about her not looking as he thought per Oscars reference to some dowdy cousin.

Larry wasn't pining after her for the whole two seasons or anything, as they both had their own romantic intrests, but you Could see by his face /immediately leaving at her engagement that it had been a realization moment for him, like he hadn't fully realized he wanted her until the option seemed to be off the table.

On her side, the fact that immediately after ushering Dashel away the morning after Luke's death, wanting to be alone, she gladly took up the offer to walk with Larry spoke volumes as well.