"inter" means "between" or "among".
"between" is used with two; e.g., the letter B is between A and C.
"among" is used with more than two; e.g., I'm among Tom, Bob, and Linda.
In almost two decades, I've never been troubled - or even noticed - that "inter" has "two meanings." Is it perhaps a case of it meaning "between" when there are two and "among" when there are three? This is more a question about (my native) English, I suppose. Is it possible to be "among two trees" or "between three friends."? I don't think so.