How can I maintain consistency in learning a new language despite a busy schedule?

Balancing a hectic schedule with the desire to learn a second language has been a challenge for me.

Well, my advice is to devote as much time to it as you think it deserves. Decide what your priorities are, and schedule accordingly.

You don't seem to need much help with your English..

I'm a big advocate of passive study. When you're doing something else (housework, eating etc), have an English-speaking radio station on in the background. You don't have to actively listen to it but have it loud enough to hear. Make sure it's a reputable station that is mostly talk-based (you won't learn anything from music!) and you'll be amazed how much better your comprehension will become over time. Also, read international news in English, watch TED talks when you've got a spare ten minutes. Try to do anything you can in English. Your English is at a high level already so, in my opinion, you'll benefit more from reading/hearing the everyday language used by native speakers than from sitting down and doing formal study with a textbook.