Well, as someone who's writing romance currently, continuing and completing a story has a lot to do the main goal.
Do you want your couple to be together in the end?
Do you want them to have a happy ending? A sad ending? Bittersweet?
Alright -- once you figure that out, ask this: what are the possible ideas that either stand in the way of that goal or move towards that goal?
@Rodimus13 Hit it right on the nose. When you asking these questions, it helps to keep a running outline of the ideas you get and organize them so that A) the story's not dragging on longer than you'd want it to but B) it's not too short where you feel it's lacking in development.
However, the good thing about slice-of-life comics is that they may or may not need a plot.
You've seen the gag-a-day comics where they have the short of the day, but they also slowly bring in small arcs. There's plot, yes, but no a full story that needs to happen. You have those arcs, and then you can ease back into strips/random stories.
Cool thing about slice-of-life is that you can kinda leave it open ending. Like yeah, the journey might still go on for the characters, but the readers will know you as the creator have closed the book on a particular chapter.