Quote Originally Posted by alan
how about the sentence as follows :

e.g. I don't know whether she loves he (or not).

can we omit the "or not" ??
I don't know whether she loves him or not. (OK)
I don't know whether she loves him. (OK; informal)

whether...or is a set pair. It's called a correlative conjunction. If 'or' is left out, that's OK. Its meaning can be picked up in context.