Good job with the epistolary format. I love the supremely snarky tone of Draco's first two letters, and the echoes between the two timelines, the original writing and Al and Scorpius discussing them. I like the angst in the mystery letters from 2017 and oh! Just the whole thing was great!
Best bit IMO:
1 August 1999 [...] If I chose to do so, I assure you, I could drink you under the table and beat you at arm-wrestling while I did it.