Is God just being mean?
No, of course not. This is not God's fault.
Once we are imperfect we can no longer come into contact with God who is perfect - it would destroy us.
The Bible teaches that when Moses had been talking with God and came down off the mountain the people who saw him could not even bear to see the reflected glory of God on his face. Moses had to take to wearing a veil after speaking with God (you can look this up in the Bible in Exodus 34:29-35).
We also discover that Moses hasn't even been speaking to God face to face - the best Moses gets is to see the back of God as God passes by. This is not something that God has done it is simply a consequence of us doing something wrong.
"Then Moses said, “Now show me your glory.” And the Lord said, “I will cause all my goodness to pass in front of you, and I will proclaim my name, the Lord, in your presence. I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion. But,” he said, “you cannot see my face, for no-one may see me and live.” Then the Lord said, “There is a place near me where you may stand on a rock. When my glory passes by, I will put you in a cleft in the rock and cover you with my hand until I have passed by. Then I will remove my hand and you will see my back; but my face must not be seen.” (Exodus 33:18-23)
How will we ever have a relationship with God if we can't even get close?
God might have left it there but this would mean no heaven for us, no life after death with God in paradise. God did not want this and so decided to do something about it. He would take the consequences of our sin on himself. He would die so that we don't have to. So God goes to the cross on our behalf to take the consequences of what we do on himself.