It is possible that The Weeknd cheated on Bella Hadid but only they will know for sure. When The Weeknd and Bella broke up in November 2016, they said the break up was due to conflicting schedules, however their schedules were never completly aligned so it sounds to me like this was a cover up.
They may have broken up for other reasons, but I have a hard time believing that they really broke up over scheduling. He then started dating Selena Gomez shortly after and they even llived together for a little while.