I agree, marriage should be an option, unless it doesn't make sense for the character, or the story makes it a non-starter. The whole thing about having bigger things on their mind doesn't make any sense. How many soldiers get married before they head off to war? How many weddings in the theater of war? They put that chaplain to use. There are tons of potential stories there if they want to tell them, around the arrangement itself (political? required or voluntary? alliances? shotgun wedding? no time like the present and you might not make it home? just want a suitable mate to run your organization with?), to say nothing of the relationship reactivity and the way different characters would approach it. If it doesn't work in the active story, I agree it shoud be an option for the epilogue, as should offspring and family arrangements in general where applicable, which all makes for great story potential, either used in the active game or later on through npc reappearances and lineage. The timeframe here is very large, beyond individual characters' lifespans.
I also agree it brings some closure for the character (if used in the epilogue), absolutely. You know that your character has some commitment to the story you set for them. I don't see any good reason why not. We're never playing the character again, the love interest apparently isn't eligible to be an LI in future games. So it makes more sense longterm if it's an option.