Crying is not only about sadness. People describe tears after a personal achievement, when meeting someone close, in response to unexpected kindness, or while being deeply moved by music. Researchers distinguish several such situations, but there is no single mechanism that explains every story.
In one case, relief comes along with joy: the long wait is over. In another, closeness takes center stage: at last you can share what happened with someone who knows how much effort it took. Sometimes the emotion is simply stronger than the way you usually express it. None of these explanations can be assigned to someone without knowing their experience.
There is no need to immediately search for “real,” hidden sadness behind the tears. And you do not have to produce the right-sized smile to prove that you are happy. You can say just what you know: “I’m very happy, and I’m crying right now.” Later, you may find words for the other shades of the moment—if you need them at all.
The stars speak. The choice is yours.