I’m so sorry to hear about your friend. This must be a difficult time for you right now. You can help your friend by having a Mass offered for the repose of his soul (remember him also on his birthday and anniversary of his death). The fact that your friend didn’t believe in purgatory, doesn’t change the reality of its existence. It’s a dogmatic teaching of the Church that all those who have died in need of purification, whether Catholic or non-Catholic, are in purgatory. That’s why the Church urges us to pray for all who die in God’s grace and friendship (CCC 1039), to offer prayers, “above all the Eucharistic sacrifice, so that, thus purified, they may attain the beatific vision of God.”
I will pray for you and your friend.