A person who is obsessed and extremely enthusiastic about the English language is often referred to as an "anglophile" or a "logophile."
Anglophile: Originally, an anglophile is someone who is fond of or admires English culture, traditions, and history. However, the term is sometimes extended to include those who have a particular passion for the English language itself.
Logophile: A logophile is a person who loves words and languages. It doesn't specifically refer to English alone, but it can certainly include someone with a strong fascination for the English language.
Both terms can be used to describe individuals who are passionate about the English language and its various aspects, such as its vocabulary, grammar, pronunciation, and usage.