I think that the hardest skill to develop when you are learning a new language is speaking. We can say that grammar, reading and listening is important too, which is true, but speaking requires more than just studying it, it requires to adjust your feelings or emotions to connect with people. You can know English well but if you can't connect with people like saying "love" without showing any emotions of love, that would be kind of weird.
To learn learn a new language and become bilingual you have to either go to a country where people speaks English or stay in your country with people who speaks English and much better if they don't speak Spanish. If you just want to know English for a different reason you can study English on your own but you are going to sound robotic. I'm still learning English.