my job is just... haylor

Absolutely.

I think 18 is Ed getting in Harry’s head and writing from his perspective, writing a song whose title could pair with 22.

By 2014, he and Harry had been tight for 4 years (since 16 and 19, respectively) and Ed called him “his rock”.

In this article below, we read some aggregate quotes.

Speaking to Yahoo, Sheeran confirmed that he wrote the tune with the thought of One Direction members' experiences in his head. He said: "I kinda wrote it from their perspective."

Talking previously about the track, the British star told Capital FM:

"I'm really happy with the record that I wrote for them. It's the first record I've actually specifically written for them.

And this is total spec but even though Ed says that Tenerife Sea was written about “him and his blue-eyes girlfriend at the 2013 Grammys”, that story does not seem to line up. His girlfriends of that era were brown-eyes ladies.

There are Sweeran fans who think Ed secretly loved her, but I never got that vibe. And when I realized that already-in-love Harry almost certainly introduced them, it clicked. Ed would NEVER do that to Harry.

So I think Tenerife Sea is from Harry’s POV after the 2013 VMA after party:

Besties, I bet you might wonder “how long has the Haylor dialogue in song been going on?” I am happy to report: from some of H’s earliest songwriting credits after their meteor-strike.

In April 2012, Taylor writes CB…BH with Dan Wilson. Later that month or in early May, she writes MIAB with Max Martin and Shellback. Both are Haylor. In them, she articulates her fears and anxieties, and her desire for him to return:

And

All she wants is for him to Come Back, to be [There].

One of Harry’s credits that summer is on Back To You, and look what he immediately tries to do: reassure her!

She’s not a face in the crowd; every single person has her face!

She doesn’t have to be terrified. There is nothing more that he’s like to do than to Come Back…Be [There] for her.

He is also hoping for reassurance that she, too, wants to stay:

But even though all the late night talking ends with “goodbye”, all he wants to do is:

Return. And ideally stay!