If he wants to understand, he will. If he doesn't want to understand, nothing you can do will make him understand. It is up to you to decide how valuable your friendship is under the circumstances.
However, friend or not, you need firm boundaries about this. Tell him firmly, "No, thank you. This is not something that can be prayed away." Tell him what you believe about God's undonditional love.
If he chooses to alienate himself from you for having boundaries, that is his choice, not yours.