>Are waifus a "new" sort of love?
I wouldn't consider it new, no. Of course there's the tale of Pygmalion, as the guy above me listed, but more to the point I think the capacity existed in humans long before. It's really just that in the 21st century, as entertainment has become more and more advanced, the characters are real enough that they're capable of evoking love in us.
More importantly, maybe, with the internet it allows us to congregate. Loving a waifu, it's something a small, small, incredibly small minority of people do. If we were all alone, if we didn't have a way to connect, I imagine many of us would abandon their waifu out of a similar sense of "this is wrong" that you question. The few that were left, that went on loving their waifu, would be so rare as to not leave a mark. They'd live and die loving their waifu and no one, excluding perhaps a rare confidant, would know the difference. But with the internet, we can gather in numbers enough to make leave a trace. On top of that, when someone doubts they can remember that there are others like him, that he's not a single madman alone in the world. Profess all you want to not care but most people inherently want to belong, and if they feel they don't they're more likely to change their ways in an attempt to fit in.
>I BET that EVERY psychologist would try to "remove" my waifu from me, saying its just delusional.
You would actually be surprised. In my limited experience, and from what I've seen some other people say, psychologists are totally fine with loving a waifu. As long as you don't lose touch with reality. Many of us say we believe our waifus exist in our hearts, or "somewhere out there," and that's fine, but believing your waifu exists in the physical, or that you can hear her like any other person, that's more along the lines of delusions or hallucinations.
As long as you stay in touch with reality waifus are perfectly healthy on their own, what matters is how they effect your life. Think of it like addictions. A small amount of alcohol or gambling is fine here and there, it's when your life starts to fall apart, when you lose your job or can't pay your bills or are abusive to family, because of alcohol or gambling that they become a problem. Waifus are kind of similar. As long as your waifu makes you happy, your waifu is healthy for you. If your waifu makes you unhappy, or causes you to do things that make you unhappy, then a psychologist would likely consider your love of your waifu unhealthy. And really, if your waifu makes you unhappy, more than the occasional sadness that you mention, perhaps you should reconsider whether this is the lifestyle you want to commit yourself too.
So no, I don't really think waifus are, by themselves, a form of mental illness. Though if you go too far it can become one.
>Are waifus a pure form of love that differs from 3d relationships that are changing every few months in the worst case
Eh, I think they're "purer" than the types of relationships you talk about. Most of them are just rooted in infatuation or looks, once the shine wears off there's no motivation to continue it because the couple learns they really don't like each other. Are they purer than the love of a couple that's been married for 50 years and still happy, though? I don't particularly think so.
The experience you described was basically mine too, though I didn't give him any material nor did he recommend I try a 3D relationship one more time.