You should ask your friend to reread the verse. It says, “We are confident, I say, and willing rather to be absent from the body, and to be present with the Lord” (King James Version). “We are of good courage, and we would rather be away from the body, and at home with the Lord” (Revised Standard Version). “We are confident, I say, and would prefer to be away from the body and at home with the Lord” (New International Version).
Notice what these translations don’t say. They don’t say that to be absent from the body is the same thing as being at home with the Lord.
If they did, they’d refute not only purgatory, but hell. You can be absent from the body and be present in hell, you know–and that isn’t being at home with the Lord.
What Paul is saying is that he’d like to leave this world and be with Christ in heaven. He doesn’t say anything, either way, about passing through purgatory on the way to being with the Lord. Someone can say “I want to be out of California and back in Missouri” without denying you have to pass through intervening states to accomplish that.
The way you quote 2 Corinthians 5:8 leaves the impression that being absent from the body is exactly the same as being in heaven with the Lord. But your quotation is really a paraphrase, and sometimes paraphrases can mislead. The verse as Paul wrote it says nothing about purgatory, one way or the other.