Okay, so here my real answer to that topic (sorry for that SoTN reference, it was too tempting):
I personally don't like the concept of "Waifu" at all. You can like/dislike fictional characters, but for me being literally in love with a character is just unhealthy. This is similar to having feelings for someone who doesn't know you and has never seen you (like a actor/actress, for example). In those case, you can develop an obsession with them, where you fabricate an idealize version of them. The difference, though, between real people and Waifus is that real people are real (duh), and therefor can do things that do not match your "phantasm" of them, which may help break that obsession a little, by showing you that what you though of them wasn't real. At this point, you can deny it, but deep down you'll always know they are not what you wanted them to be.
Waifus, on the other hand, are not real, and their "character/lives" are limited to whatever material they are from (game, anime, novel). If you fall for a Waifu, you know she will never change (unless they are in newly released material). She will always be that character you are in love with, and since her "character/lives" is limited, you can always fill-in-the-blanks with whatever you wish (the classic example is making the Waifu horny even when there no indication at all of that officially). The Waifu will never break this "phantasm" you have. Worse, some fans that have the same Waifu may reinforce that "phantasm" by making artwork of it (like those Fusu post, for example). This is why people like them, they are "concept" that are vaguely defined, and can be slightly-changed to match each of their taste. It is much easier than having a real relationship where the person may betray your "idealize" version of them and I am no expert, but isn't this a necessary step toward a real healthy relationship? To accept the other, for both the goods and the bads? Isn't it a bit childish to consider only the good?
I never had any Waifus, but I do have some fictional characters I like. Let's pick the Touhou project as a example, I quite like Satori in Touhou 11. I like the concept of someone able to read mind, and becoming a bit "jaded" (translation of tired + indifferent) because people are predictable and nothing can really surprise her (she also isn't shy to use her ability at all). In her boss theme, there's a hint of creepiness', which shows why people avoid her (and in the game, the theme picks up exactly where she becomes serious). In her stage theme, there's a hint of lonliness, which could both means she's lonely or simply that her Palace is lonely because there's no one there except her (and some animals). Now, how did the fandom turn her into a Waifu? By focusing only on her "lonely" side, and making up that she want someone to comfort her from that loneliness, completely disregarding the fact that 1) She isn't that lonely, she has pets that don't mind being around her 2) She ain't horny, way too "jaded" for that 3) They wouldn't last a day having their mind being read against their will (everyone has secrets). Now, I know this is all fictional, but if you reconstruct a character so that you'll love them, taking only the parts you want, ignoring what doesn't match your taste, making up what that character would tell you (as oppose to someone actually talking to you, possibly challenging you), can you truly say you love them? Aren't you just loving your own image of them? This is almost like saying "I like sushi, when it is covered in chocolate and there are no sushi in it"