First of all I suck at these, so I’m sorry in advance for whatever might come, they probably won’t be that elaborated. Second a few of the headcanons that I have basically turned into canon because this fucking show is just unbelievable, like they really went there. It’s like the writers have been looking for stuff on tumblr and ao3 to use it on the show. But here are a few that I have.
They like to have dinners at least once a week in Magnus’ balcony because they like to watch the stars and people in the street (also because it’s really romantic).
During one of these nights, Alec insists on making the dinner and preparing everything. After they finish eating Alec shakily takes a little box out of his pocket and proposes to Magnus.
Magnus has a folder on his phone just with pictures of Alec smiling, because, damn, he has a beautiful smile that always melts his heart.
Alec has one as well.
(This one is actually one of my favorites) Magnus volunteering to help Alec train and Alec thinking Magnus would be a bit inexperienced in hand-to-hand combat - because he’s a warlock and he doesn’t really need to know how to fight when you can use your magic, right? wrong! - and he ends up kicking Alec’s ass.
They definitely never miss a Pride Parade.
Alec wears a rainbow flag pin everyday during Pride Month.
They sleep holding each other’s hand.
They actually love doing mundane things, like going to the movies.
They take Madzie to watch Wonder Woman. Alec leaves with a crush on Chris Pine.
Alec borrows a lot of Magnus coats/jackets and suits. The less flashy ones, of course. A few of his shoes too.
Alec calls Magnus “love”. Magnus calls Alec “babe”.
I think those are the only ones coming to head now. I’ll add more if I think of it.