I see many sentences with and without "to" in sentences similar to the following.
If you need (to) keep using it, you don't need to return it to me yet.
Are both (with and without "to") correct? If yes, are there any differences in their implications?
In my experience, AmE tends to retain the "to" in most such cases. There may be exceptions, but in your example, I would not remove the "to".
[It is common, however, to omit "to" (ie, use the bare infinitive) in negative constructions: "You need not return it yet." But that's not what you asked about.]
