One common theme is family opposition. For example, families might not approve of the relationship due to caste, class, or economic reasons. This often leads to separation and sadness. Another theme is distance, like when one of the lovers has to move away for work or other reasons. And sometimes, fate plays a cruel role, like when one of the lovers falls ill or dies, leaving the other in a state of eternal grief.
Common themes include unrequited love. There are cases where one person loves the other deeply, but the feelings are not reciprocated. This can lead to a great deal of sadness. Another is the theme of lost opportunities. Maybe the lovers didn't confess their love at the right time, and then it was too late. And cultural and religious differences can also play a part. If the lovers are from different religious or cultural backgrounds, it can cause problems and end up in a sad separation.
Well, in many love sad Hindi stories, the theme of sacrifice is prominent. One of the lovers may sacrifice their love for the well - being of their family or for some greater good. Social status differences also contribute to the sadness. If a rich person loves a poor person or vice versa, society's norms can create barriers. Also, misunderstandings can be a theme. A simple misunderstanding between the lovers can lead to a break - up and a lot of heartache.