Actually, classical guitar music is heavy with all kinds of musical devices you will learn about in the theory of music. Augmented sixth chords, secondary dominants, borrowed chords/modal mixture, secondary diminished seventh chords, Neapolitan chords. Here is a short list of examples, some of which may have already been mentioned. It+6: Giuliani, Op. 48, No. 23, ms. 36, Carcassi, Op. 6, No. 13ms. 4, Op 21, No. 23, ms. 3, Sor, Op. 31, No. 20, ms. 4. Fr+6 Sor, Op. 1 No. 56 before the repeat. also a beautiful example of chromatic writing that includes in this 8 measure passage suspensions secondary dominants, borrowed chords, and other chromatic devices. Legnani, Intro Theme, Variations and Finale4 before the fermata. Giuliani, Op. 122, Fantasie kon Themes of Rossini. Carulli, Op. 330, Variations on La Marseillaise, 3 before the whole note end of the variation 1 I think. Ger+6- Sor, Op. 6 No. 1, 4, Op. 2 No. 3. Also a beasutiful example of chromatic writing. The passage contains It+6 as well, and many secondary dominants. Op. 2 No. 6.
There are too many to mention in a short reply. If I may be so bold, I've taught college theory for 30 years, and actually am in the process of completing a book, (Music Theory with the Guitar). Let me know if you (or anyone) is interested. I've spent my life looking for these things.
In short, the guitar composers of the classical and romantic era (I didn't mention Aug 6's by Tarrega, Llobet, Bosch, Sagreras, etc.) were just that, composers, who used the melodic and chromatic devices of the craft, and just happened to be guitarists. Their compositions were written in the common practice style just as those for piano, violin, etc.
More good advice would be to do a harmonic analysis of the pieces you study with your teacher. You will discover many tings about the structure of your music.