Paul talks about the conflict which existed between him and the people in Corinth which has now been resolved. Paul was suffering from the conflict because he cared about them and wanted the problems to be resolved. That suffering forced him to confront the issue in ways that caused him pain, but had a positive result.
When there is conflict in a relationship, it is painful to address it. Ignoring it turns out to be an uncaring response. If we cared for the other person, we would want it resolved as soon as possible. In 1 Corinthians, Paul taught love, but love sometimes requires directly talking about an issue with the goal of restoring the relationship.