Complex sentence: At a bathhouse, he met new friends, one of whom had a communist family background and, as a result, he began listening to enemy radio broadcasts; these were strictly forbidden in Nazi Germany, being considered a form of treason.
Split into simpler sentences: At a bathhouse, he met new friends, one of whom had a communist family background and, as a result, he began listening to enemy radio broadcasts. Listening to enemy radiobroadcast was then strictly forbidden in Nazi Germany, being considered a form of treason.