This is by far possibly my favorite scene in the entire series unless they do something similar in the future. The music absolutely gets to me, Diane is so sweet but has a certain kind of edgy jaded voice to her at the same time which is exactly what you would expect for Rick's taste and for what he's like. She seems so naturally intellectual and smart at least on an emotional level and Rick is so whipped and almost endearingly apologetic compared to her; she seems to have a certain kind of natural confidence about her that Rick respects and brings out how sappy and gentle he actually can be. They do seem like they're perfect for each other, they both have those tired bags underneath their eyes and are worn and sweet, jaded but romantic and gentle and seem to have a drinking problem and seem to be impulsive in the same way-and the fact that knowing even though they're having this conclusion and heart to heart but there's really no a genuine way for Rick to tell her these things in real life and that he can only dream about it or have surreal experiences like this every now and then just makes the parts where he tells her that he can't let go of her or move on even more human.
The reason why I'm so melodramatic about Rick's backstory with Diane and his love for her is because it's so real and human; I know a lot of people and hear of a lot of people and have experienced it myself what it feels like to love a singular person so deeply for a reason that you can't explain and literally cannot let go no matter how many years pass. It's so wretching. This is old Disney movie level scene magic.