To readers, the new event isn’t a big deal for your character because your character felt the same way when they were cheated on as they did when the dog peed in the house or they were late to work.
Using synonyms for words that express feelings and emotions can help readers understand more about who your character is through their emotional responses.
Showing the degree or level of emotions and feelings will allow you to further develop your character and show what is more important to them. A character might be upset the dog peed in the house (a minor issue) and frustrated when they were late to work (more important). When their significant other cheats on them, a character might be irate or furious (major issue).