The passage in question is this:
友達はかねてから国元にいる親たちに勧まない結婚を強いられていた。
Now, I recognize that kanji from 勧める, so I'm inclined to think this passage means "For some time, my friend had been pressured by his parents back home for his unadvised marriage" or something like that, but Denshi Jisho doesn't come back with any results for すすまる, and I've not encountered it elsewhere, so I'm mostly inferring this from the kanji and context.