So many films end with a loved up couple, few would last the distance.
Here's my take:
Ariel and Eric (little mermaid): she would miss her merfamily (strange as they are) and it would be a massive culture shock for her. He'd get annoyed that she didn't understand Danish aristocracy and social protocol. She's 16 ffs! She'd realise there were plenty more men with legs out there, it wouldn't end well.
There must be loads.