That weird dialogue option is always there. The one where you say you two never pursued a romance, or whatever. It’s not a “game over” for the relationship… It’s a straight-up bug. There are dialogue options available that simply aren’t relevant. So I wouldn’t read too much into that.
I also wouldn’t overthink getting the scene to trigger. For what it’s worth, I have triggered the scene without ever talking to the Sharran lookout. You just need to long rest. More than once before you leave Rivington/Wyrm’s Crossing. You two do go “down by the river” after all.
If you fight all of the battles that are available, you can certainly long rest multiple times while you’re in this area. If you don’t long rest, you really can’t complain about missing scenes.
