Jonathan Sims, Head Archivist of the Magnus Institute, London, is Demiromantic, and I will die on that hill.
If we’re talking headcanons, he is Aromantic to me. To me, as someone who doesn’t really like JonMartin, Jon yearning for Martin in season 4, is less “I love that man, and have secretly been in love with him for some time” and more “Martin is the last thing I have of simpler times, when Sasha was alive, when Tim was alive and didn’t hate me, when the worst thing I had to deal with was misfiled papers.”