Wow. That was awesome if you shot this yesterday and edited it by today.
I have a few suggestions on the VO (voice over. Voice that comes in as narration from someone who is not on screen):
Make their voices live in their own space. Don't record them outside - make the listener feel it's voices from inside their heads.
Check this short project done 5 years ago:
https://www.youtube.com/watch?v=
See how the voice has it's own space? I wanted to make the listener feel like the guy was whispering into your ear real close/intimate. And the ambiences are whispy and tons of verb. That's more like how I would treat this short film.
I would smooth out the fade in/outs of the ambiences you do have in there, like the ending ambience. Also the beginning one. Possibly a few piano notes could add to the mood? Nothing big, something small and special - heartfelt.
Also, after the very first shot, it shows someone in a white shirt in the middle of the screen - I immediately thought this was your protagonist. Then it showed a cute couple all around London. Maybe show a bigger shot of a crowd not focused on anyone? That unless you were pulling a Peter Jackson or Steven Spielberg and that's YOU in there - hehe.
Great job!