Kriselle and Ralsusie are the canon pairings, and here's how the game ends on normal route.
The big tragedy of deltarune will be Susie forever cutting herself from the lightworld, and be the sacrifice in order for the darkworld to continue existing.
She saw the prophecy, and it was the death of the dark world and all people in it, thus why she got so angry, and that's why Ralsei wants Kris and Susie to not care about him.
The ending will be Kris and Susie hugging each other as they say goodbye to one another.
> Susie stands at the top of castle town, with Ralsei next to her, both of them look at the mysterious skies of the darkworld.
> It then cuts to Kris and Noelle, sitting in front of the lake at a late night, Kris looks down on the lake... and the screen goes black.
> With two sentences appearing one after another.
> "Goodbye, Susie..."
> "Goodbye, Kris..."