Judas didn’t believe what Yeshua taught and commanded, and that is what is required to qualify as believing in the context of the word of God.
Believing on someone doesn’t simply mean believing they exist. Satan so believes!
Is this what you’ve hung your hopes on?
.
So Judas sold Jesus out - he abandoned Him.
Did not Peter do the same?
Scripture does not record what Judas 'believed'; merely what he DID.
Peter wept bitterly - Judas hanged himself.
We have NO idea if Judas' last words were similar to the penitent thief or like the other one.