When someone has a tear falling from their right eye it means they are happy and if they have the tear falling from their left eye it's sadness.
If both eyes are teary it can either be sadness or happiness or frustration.
Many people will start crying when they are happy and the right eye is where the first tear usually comes from and after that both eyes can start producing tears as well.
But sometimes only the right eye will shed a tear which means they are happy and excited about what is happening.
If the tear starts coming from the left eye it means they are likely sad and upset about something.