In the Half-Life Universe all manners of strange things occur. Yet, most of the time those occurrences are consistent with content within each game, and from episode to episode, and game to game.
In HL-2 Episodes 1&2 we are privy to the developing attraction, if not subtle flirtation, between Alyx Vance, and Gordon Freeman. Even Alyx's dad, Eli, would approve of a marriage (or at least their doing their part to repopulate Earth). We also get some of the back-story and current status of the Borealis, and an imperative to destroy it.