Will i need a crown if cusp of my molar has broken off?

Not necessarily: Have your dentist evaluate the tooth for the proper restoration. Can't tell over the internet how bad the break is.

Usually: If the cusp is one of the main chewing parts of your molar, by all means.

Perhaps: These types of questions cannot be properly answered over the internet without actually being able to see the tooth in question, evaluate the occlusion and see an x-ray of the tooth. Most teeth where the cusp has broken off are better off having a crown rather than a filling, although that is not always the case.