Unless you're under some kind of contract, you have your answer. What is holding you to this current job?
I'm not sure if this is the case, but OP may not be aware that some employers offer part-time remote internships, or the employer who OP interned for at triple his current pay may not have offered them.
OP, if you read this and this is the case, I went through a similar experience. My first internship was for a Silicon Valley company over the summer, and then I went on to work as a System Administrator for a college when I got back to school at ~33% of what I made over the summer. However, for my next internship, I worked for a different company and when I went back to school we agreed that I would work part-time remotely. I still made the same per hour as when I was working 40 hour weeks, I just worked fewer hours. I had a bunch of friends who did the same thing - interned for a company for a semester and then returned to school and worked for them part-time for a lot more than they would have made if they'd worked for the school.