Key Switching

hello Muris, first off i would like to say im a long time fan of yours and your lessons. good stuff. my question is i have this chord progression that uses Bm F# G D. when i started playing with the chords i was playing in the key of dmajor. So that F# should be an F#m but i for some reason thought it sounds great as a major chord instead. would this be a switch to the relative harmonic minor? i usually dont question these things but i would like to better understand music. also if this is the case can i use the harmonic minor scale over the chords that are derived by that scale (G Bm F#) and switch betwwen the major scale? sorry if im not being clear.