Rajnath killed Arnab ... It's hinted during Dev's attack
May be sakshi had a proof against Rajnath , by using it she blackmailed Raj to marry her...
May be later she fell in love with Rajnath( sakshi has said"main ne bhi kissi se pyaar kiya tha" , I think it is raj only). Rajnath cheated sakshi , caught with some other women. ( sakshi always doubt Rajnath regarding this. Still she feels secured because she holds Rajnath secrets).
Sakshi knows more secrets of Rajnath revealed during shaurya blackmailing raj.(even though we don't know what secrets).
Rajnath and sakshi patched only because shaurya ( once sakshi mentioned about this)
Tomorrow how RajMa affair effect Sakshi... Let's wait and watch