This was inspired by the song Forever Changed by Carrie Underwood in like, the vaguest sort of sense tbh? Like the content of the song basically didn't have any effect on it, as much as the song title itself did tbh, but still.
Forever, in Magnus' opinion, was made up of a plethora of very mortal moments. It was fighting wars that wouldn't matter in a decade, in a century, falling in love with people who wouldn't live to see the next decade, or who would grow bored of him within the span of the next year or month; it was drinking with new and old friends on nights when the world was too gloomy to do anything but throw a decent party for everyone to lose their cares to.
It was new generations of friends he had made a hundred years ago, and reflecting on how much the descendants were alike or different from the person he had known and loved so long ago. It was catching bits and pieces of himself in the world around him, in the friends he made, the people he helped. He lost and found himself a million times over in all his years, and it was a very mortal process the whole time, rediscovering who he was, and then uncovering the fact that he didn't know a damn thing about himself at all.
Forever was falling apart because God, he was really going to live forever, wasn't he? He was really going to have to go through this cycle again and again and again? And even though the world seemed to change all the time, it didn't—not really. Everything that cursed humanity was caused by the same things no matter the year or century: love, pride, and greed ruled all, and it caused war, and heartbreak, and death, and destruction, and loss.
And it was so God damn tiresome to watch the same things that plagued humanity curse the Shadow World and Downworld too—it was especially tiresome to have to go through the same thing with immortals like himself, those who had witnessed just as much—if not more—than he had, who should have learned from history and their own mistakes and who should have fucking known better—forever was being subjected to the same stupidity year after year, no matter which world he was playing in at the time.
But, forever was also more than that, wasn't it? It was love—love in its purest form.
He had a million memories, and even though some stung to think about they were still his memories, and he had earned them, had earned all the pain that was caused by them, because they had given him the greatest of joys, once upon a time.
Forever was his friends that he had known for decades, who he had fought in wars with, who he had gotten drunk with when they had been heartbroken or grieving the loss of one of their other friends. It was all the people he had fallen in love with—and God, did Magnus love to love. He loved to love warlock and seelie and mundane and vampire and everything in between. He had so much love to give some days, some decades, that he felt like he was doing the universe an injustice when he was nursing a broken heart and not loving to his fullest.
Forever might have been something no mundane could ever know, but the essence of it, of Magnus' existence, was very much so theirs. Love and hate, ups and downs, and everything in between.
And Magnus thought he was doomed to it, doomed to the stagnant variation of it—as much of an oxymoron as that might have been—for, well, ever.
Not to say that it was boring, but, well, it took its toll on a warlock, knowing, in his good decades, that a century of pain and heartbreak was just around the corner. And with every one that came, with all the pain, he felt himself wearing down. Eventually, the hard times would get the better of him, because he was going to let it. He was going to let his immortality, and the universe he played in like it was nothing, get the better of him. Because that was what forever did: eventually, it got the better of you. He had seen it time and again with everyone he had ever let into his life, and he had long accepted that it would get the better of him too, one day.
And he was ready.
God, he was so ready.
But then the universe surprised him, and it gave him one Alexander Lightwood. And suddenly… all the centuries of hardships and heartbreak he had experienced were worth it—with one small action, one small gift, the universe made up for every absolutely shitty thing it had ever done to him. And all it had to do to make up for it all was put him on the same path as Alec—that was all he was going to ask for from it, that he stay on the same path as him, because God damnit, Alexander was his soul mate, and if the universe tried to take that away from him, it would feel his wrath in whatever way he could bring it upon it. One way or another.
But suddenly the forever that was laid out in front of Magnus looked more like… well, like Alec. Putting aside the fact that Alec was very much so mortal—maybe he wouldn't always be, maybe they would find a way around that, maybe the universe would deliver even more miracles for Magnus and his Alexander—it was easy to imagine decades upon centuries with Alexander at his side the entire time. It was so God damn simple to see a lifetime of loving Alec stretched out into his forever—their forever.
He could see himself waking up in bed every morning next to him, and marveling over the fact that he got to wake up next to the love of his life every single morning.
He could see himself going about his day, his work, with Alec on his mind, could see himself fighting in wars with and because of Alexander, could see them raising a family together, could see them moving cities in much the same way Magnus had always done—but, the difference being now, he could just as easily see himself staying in New York with Alec if that was what they decided would be best for their family. (He was already thinking of a family they didn't even have yet, so prepared to give Alec his everything, his existence, his forever.)
And if Alec couldn't share that forever with him? He saw nothing but grief in his future after he was gone. He would share Alec's life with him, and when the universe so cruelly snatched him away, he would spend the rest of his forever in mourning, and it would be the sort of mourning that drinking and partying with his friends would not be able to pull him out of.
Either way, forever would be a different sort of existence now that Alexander had been dropped into the middle of it, and with every fiber of his being, Magnus hoped that for once, the universe would just let him have this, would just let him enjoy one nice thing without feeling the need to punish him for it, without needing to take it from him after letting him have a taste of something nice.
Magnus just wanted his forever to be full of love, full of Alec. God, he just wanted the good kind of forever with his soulmate, and after everything the universe had put him through, he didn't think he was asking too much in that.
But Fate was a more cruel mistress than the universe itself was, and in the depth of his soul, Magnus feared she would take Alexander away when the universe would grant him to him.
He tried not to concern himself with Fate too much on days when the universe was already tearing away at his hope and patience, though. For now, he had his Alexander, and he had to be thankful for that. He had to be.