[General] no longer

[aya_aya7121]

Dear teacher

"I no longer feel confident"
I want to know what function of no longer is

Thanks

[colloquium]

No longer = not any more.

It indicates that something happened or was in a certain state in the past, but has now changed and cannot be described in the same, past, way.

It carries a meaning similar to used to, which describes something (an action or state) that doesn't happen any more (which has ceased) or is no longer true (I used to play football: action; I used to be fat: state).

Your original sentence can be paraphrased as:

I used to be confident, but I am not (confident) any more.

or

I was confident, but I am no longer (confident).