@albirew "My partner" works in a couple. But since they're acting like a fairly recently formed couple, "My love", "My beau", "My boyfriend/girlfriend" would be among things I'd expect.
"My lover", I won't say its scandalous what with the context, but it gets about the same value as "My fling" (my sexual partner without deeper feelings or at least without any particular intention of permanence). Come to think of it, since a "fling" is usually used in a summer vacation context, and they might only have intended to be together inside the game for as long as it lasts, and most MMO games last only a year or two (the longer lasting ones are the 'winners'), then 'fling' or 'lover' might be just the right word. But "game wife" and "game husband" would also have been the right words in that case, and maybe less scandalous for some