Johannes Brahms didn’t plan to have an affair with his mentor’s wife; it just sort of happened. It was 1855 and the composer was 21 years old, the handsome protegé of Robert Schumann. Pianist Clara Wieck Schumann was 35, left alone to raise seven children after Robert attempted suicide and went off to live the rest of his unhappy life in an asylum. Brahms moved in to help Clara out, and soon he fell in love. Judith Lynn Stillman & Friends from the Rhode Island Philharmonic Orchestra present Mystery, Madness and Music, a multimedia concert exploring this intriguing, tragic love triangle. The concert happens Wednesday afternoon at RIC and Sunday evening at the Philharmonic Music School in East Providence.