>>172258 (OP)
If your waifu comes from a piece of media where she has a romantic or sexual partner, likely she would still love the guy/girl she was with in her native world of fiction, and if she didnt she'd likely prefer somone who is most like her lover in that world when she comes to this world.
But even if that were true, she'd not be as appealing as a waifu for you, she might be cucking her canon lover with you, or perhaps her love for her canonical partner was part of why you had loved her to begin with. She might not be your waifu wothout her love for her canonical mate.
Just think about it.