What is the saying or idiom or word that means when "friends" don’t need you anymore it seems like they don’t know you anymore

"a fair-weather friend" is an idiom.

• "someone who is your friend only when things are pleasant or going well for you" TFD
• "loyal or helpful only during times of success and happiness" Merriam-Webster

You could also say "an opportunistic friend", "an opportunistic friendship"

The term I would use is "false friends."

"What you mean, 'We,' kemosabe?"

This [the following additions, to obey the site's rules to the letter] is very much like having to explain a joke after you've told it, but Howard Schweber writes at The World Post, 1969:

In a classic Mad Magazine cartoon ... the Lone Ranger and Tonto are surrounded by a horde of hostile Indian warriors. The Lone Ranger says to Tonto "what do we do, now?," to which Tonto replies, "what you mean 'we,' kemosabe?"

[Tonto usually referred to his senior partner as 'kemosabe'] [and the 'real' Tonto wouldn't have dreamt of such disloyalty]

The joke is old and quite well known. At the link Punchline Regularly Tossed Out Without the Jokes They Come From, 'Chanteuse' adds: 'I always heard this said, "What mean WE, white man?" ' I came across it recently in one of Trow's Maxwell novels.