It depends on what do you mean by "learn" and (especially) "fluent".
Do you want to be able to have full, substantial adult conversations with people? For example, do you want to be able to say something like "I wouldn't have booked a return ticket if I'd known that I was going to meet all you great people and have such a wonderful time here, but I'm sorry, I have to go home now", with the conditional and the subjunctive correct? Or would it be sufficient to say "Thanks everyone, but I must leave now", with everything in the present indicative?
Do you want to be able to watch a gritty TV series that has a lot of swearing without subtitles? What about a rom-com? Or the TV news?
Do you want to be able to read a novel without looking up more than one word every 20 pages? How about every 5 pages? Every two paragraphs?
Basically, what's your endgame? And how committed are you to it, really?
I ask because I speak four foreign languages with differing degrees of fluency, all of them acquired by spending 2/5/10/20 years in another country. Acquiring true fluency — the kind where you don't have to think — is hard, and requires lots of time, whether you prefer to learn by osmosis or by bashing away at the grammar books. I am properly fluent in two of the four languages, but not for the ones where I spent less than 6 or 7 years in the country. Forcing yourself to do it in an English-speaking country is going to be hard. Getting a partner from that country is the best shortcut if you can't move there!