Bilingualism is a bit overloaded nowadays, which I find kinda annoying given that word “polyglot” exists.
Anyways, if you can freely use another language in an informal exchange with a few people of different sobriety levels while failing to remember key words and recovering from that - you’re a fluent polyglot. Ability to exchange information is a key part of what language is, and that’s how you measures your proficiency.
Bilingual can also mean “natively proficient in two languages”. And if you’re older than three years old and are not native speakers of multiple languages already, the chances of you becoming one are slim.
Native proficiency is a result of a language acquisition ability that is not well understood and disappears early into child development. It results in a level of effortless mastery that seems to be impossible to achieve as an adult, i.e. a dedicated or merely attentive native speaker will be able to recognize that you are not one.
“Permaban” is the word you’re looking for.