Act 3 - Murder Tribunal. If playing as Durge, you can find this interaction with the echo of Amelyssan, [former high priestess of Bhaal] - that confirms Ascended Astarion's "lovers forever," comments. She throws in that you'll be cuddling as the stars collapse from the heavens. IDK what this looks like in Faerûn, so I threw in an animation from NASA.
Core collapse supernova animation is from NASA, here: exoplanets.nasa.gov/resources/2174/core-collapse-supernova/