I don't know enough detail about you or the kind of person your step-dad is to advise on such a serious stituation. You seem to be a kind person or you wouldn't feel an guilt for screwing up any of your step-dads life.
I say, just make the choice you feel is right and believe won't leave you with any regrets.
I say, just make the choice you feel is right and believe won't leave you with any regrets.