Parasocial relationship
The term parasocial relationship was coined by sociologists Donald Horton and Richard Wohl in their 1956 "Mass Communication and Para-Social Interaction" article. It describes where a person imagines having a relationship with someone they don't know, such as a celebrity, influencer, YouTuber, Twitcher, or fictional character.
For example, a person may frequently watch a streamer on Twitch and interact with them in chat so much that they feel they have a relationship. However, while you can interact with someone with hundreds, thousands, or even millions of followers, that person can't have a real relationship with every one of them.
Parasocial relationships are fine if the person with these feelings realizes the relationship is one-sided. However, these relationships can become dangerous if they interfere with real-life relationships or lead to behaviors such as obsessing, stalking, or even kidnapping.