Describing these types of relationships in just a few sentences isn't exactly easy, as there isn't one general definition for it. Often the concept is named "Waifuism", which is a loosely defined term for relationships of this kind. The general idea is it loosely describes a phenomenon where individuals develop genuine feelings of love for fictional characters and form relationships with them, which is treated of equal importance and weight as a relationship with a 3D person would be. Naturally, these relationships don't the same as it would in other relationships. Luckily, the human mind is incredibly powerful, and through means of imagination, lucid dreaming and similar, it is possible to feel close to one's partner(s) regardless of those limitations. It certainly isn't for everyone and is a decision that requires careful consideration.

There are several communities on the internet that have formed to accommodate waifuists and similar and drive discussion and support among them, each with their own distinct rules and values. Unfortunately, these communities often face misunderstanding or outright hostility from the outside, because of the difficult to relate to nature, as well as some individuals that have shed a bad light on it through questionable actions. It is of course understandable, that being in love with someone 2D, and devoting your life to them, is not something everyone can or will understand, but it's important to adopt a "live and let live" mentality and appreciate that it brings happiness to those involved.

Waifuism itself lacks a clear, static definition, varying widely among individuals, with some living a more scientific approach of viewing their partner as non-existent in any form, while others will take a more spiritual/esoteric approach to things. For many it's also something in between, in the end waifuism is a broad term with no static definition. Happiness doesn't look the exact same for everyone, and it is a diversity that should be celebrated.