I think always turn to the Word of God, that will guide us. You will need to show him out of the Bible what God says about these questions. Knowledge of the Bible is key. In this way you will help him find the truth.
(I did not study Christianity at a university, but it will be wise to ask somebody that did study further on this subject, as they have a better understanding, to assist in get a better understanding). So in this way God is helping you through your friend to get a better understanding of His word. If you fear that he will influence you wrongly, it will be best to avoid him.