One thing to think about: Christians (and most people who ascribe to some sort of religious/supernatural belief) bring an entirely different mindset/lens to their thinking and perceptions of the world.  Their worldview is, in large part, based on fear, and their compulsive beliefs in their own inferiority and worthlessness. They are told their ONLY value is in “God” and that without GOD they are nothing.  They will spend their entire life attempting to overcome this sense of “worthlessness” in many different ways. Some choose to become “super Christians” spending countless hours in prayer, Bible Study, and church attendance. Others will attempt to defuse these feelings of inadequacy by defending their faith and attacking those who don’t believe. Still others will project all of these confusing emotions onto everything and everyone around them.

My point is that, as a non-believer, you simply can’t see this as simple religious differences. It goes much, much deeper. You may want to point out to him what his own Bible says about being “unequally yoked”.

Good Luck,

Steven