they also don't double-dip, as a rule, and Maedhros in specific has inherited Remarriage Trauma

I've seen fic scenarios where an arrangement of some kind was worked out, but he wouldn't without Fingon's presence and explicit consent

I'm not saying he's Unshippable, but frankly his fidelity is probably the only thing, in his entire life, that he doesn't hate himself about

(he does hate himself about the marriage, about letting Fingon bind himself to him)

(between the Doom and the quasi-incest, he can manage to feel awful about even his love for his husband)

this mostly means that he just - I don't think he'd be able to "do that" to anyone else, in his hyperdespair state