...but then, so did Peter.
And so did the other disciples during the time of Jesus' arrest up through the Crucifixion.
And if we get down and dirty about it -- all of us have betrayed Jesus at one time or another, even as "practicing Christians."
If we get REALLY honest -- there's a bit of Judas in all of us, because we're all capable of doing the expedient thing, instead of the honorable thing; and we're all capable of selling someone or something out for some cheesy, short-term good.
Notice, however, that Matthew 27:3-5 states: "Then Judas, who betrayed him, when he saw that he was condemned, repented himself, and brought back the thirty pieces of silver to the chief priests and elders, saying, "I have sinned in that I betrayed innocent blood." But they said, "What is that to us? You see to it." He threw down the pieces of silver in the sanctuary, and departed. He went away and hanged himself."
If we're honest, most of us have done things to other people, for some short-term gain, which blew up in our faces and caused us tremendous pain, even to the point of wanting to do ourselves in. "Satan" has entered into each of us at some time or another, even as we were professing Christians.
If Jesus is capable of forgiving us, He is certainly capable of forgiving Judas Iscariot.