Only Ron stood by him. "They'll all forget this in a few weeks. Fred and George have lost loads of points in all the time they've been here, and people still like them." (15.20-21)
Here, Ron shows temporary and long-term loyalty to Harry, supporting him in a tough moment by acting like his friend – at a time when no one else wants to be – and encouraging him that, down the road, people will forget about these lost points. He argues that if Fred and George can keep their friends after losing points time and time again, that Harry should be able to also.