Have you ever said or had this said to you?: “Let’s remain friends…” 
That’s usually what a person says to another person as he/she is breaking up with the other. The special relationship has come to an end, and one says so when he/she wants to move on.  
Can we say that to God? Can we say, “God, it’s been nice. But I cannot let you be my all in all. I found other things/beings that I want to explore. But I still like you lots. So, can we just be friends?” 
God says “No!” Why? Because we are calling Him a liar!  
If you reject me, of course I will be hurt, but it won’t have dire consequences to you. You may be moving on to better or equally good things as me. And I have to accept that. However, when we move away from God, what we are saying is that He is a liar! 
Why? Because God made promises to us about our future lives in Him. But when we move away from Him, we are in fact saying that His promises are not true. That, there is something better than His promises. What is that but unbelief??
“The one who believes in the Son of God has this testimony within him. The one who does not believe God has made Him a liar, because he has not believed in the testimony” 1 John 5:10-11You cannot just be friends with God. Either He is your all or He is nothing to you!
PH