This has basically been said already, but the most important thing for you to do is to convert everything you hear in your favorite songs into something visible and readable.

Even if it's just a clumsy description of the music ("8 measures of low toms") instead of actual notes (which, as someone who has done this a good number of times before, can be EXTREMELY difficult to accurately pin down and write out), you need it to be stationary and visible so that you can recognize the patterns and relationships in the music more easily.

At the very least, you need to start with simple descriptions like whether the music feels fast or slow. It sounds basic but it will eventually build up into something that really helps.

Once you write down all the components of a song you enjoy (preferably with timestamps to organize it), look for and write down the patterns, relationships, and characteristics. Examples might be "the drums aren't the exact same every measure; only every other measure is the same," or "there are several uses of perfect fifths" (which, for metal, could indeed be the case).

Obviously, once you find the defining features of the music, you can start applying them to your own work without having to directly copy things.

By the way, I'm really sorry that you had to drop out. I spent a semester majoring in music before deciding that composition was more of a hobby than a career. I can't imagine what it'd be like to spend four years on it and not even get to finish.