You must mean, How does one separte himself from God? In a word, "sin".
And much as leprosy, which starts off as a red rash, will soon be white as snow if not checked in time.
Yes you're right, sin separates us from God. The opposite from light is darkness, and darkness is away from God. And to carry on wilfully sinning when we know God is to turn from him, we are cast out by our own lusts. I also believe that the soul doesn't die. We have a chance now to turn from sin and deny ourselves, and Jesus has showed us the way and came as a perfect example for us to follow. If we follow the perfect cornerstone, then the building will be straight.
I thought about this the other day. When the cornerstone is laid, a bricklayer then measures every brick with a spirit level to make sure it's straight to keep the building straight. Our spirit level is the holy spirit, and he's measuring us and correcting us to be in line with our cornerstone which is Christ. If we obey him and turn from sin and keep the word of God pure then the building of God will be built perfect on perfect foundations built by the hand of God through the spirit and not by mans hand. How can we be used to build the temple if were crooked or broken? we can't. And we will be cast away. Just like being grafted into the olive tree and then cut off again if we're not continuing in goodness.
Romans 11
For if God spared not the natural branches, take heed lest he also spare not thee. Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in his goodness: otherwise thou also shalt be cut off.
And to be cut off from God is to be in darkness, if we're in darkness we can't see. And our guide is Satan and he pulls us down, just like being in the depths of the sea on a dark night, being pulled under and we can't escape, seeing light in the distance, but we can't reach dry land. Because Satan has us in his grips.
Like taking drugs, apparently it feels great at first, but eventually it takes hold, and once addicted you're in a terrible way. The world seems wonderful with wonderful attractions but the more we are in the world, the deeper we are pulled in, and the more the fruits of the spirit disappears and are replaced by the works of the flesh again, until be are back in darkness, feeding on our own lusts. These are what we are to deny, the lusts of the flesh and turn from sin to walk in the light of God. Like you say sin is like leprosy that gets worse and worse if not dealt with.
And if we are in the depths of the sea, then Christ is our life ring, and he can save us. He can pull us out of those depths. I always think, what would Jesus do. I go back to the cornerstone to make sure I'm right. He is the only true way and the only truth, his is the only life to follow, and through going to God and repenting and turning from sin again, and praying hard to God, we can be pulled back into the light of life and away from darkness through Christ.
God's people shouldn't want anyone to go to hell, but have hope that we can bring everyone God and heaven, no matter how deep they are and how far away the seem. There is hope for everyone, even if they come to God at the very end of their lives, like the thief on the cross, with God, all things are possible.
We shouldn't judge anyone, just bring them the word of God and that will judge, and if we can't speak to them because they won't listen, then live it out in front of them, showing them the love and mercy of God through our lives and bring Christ to them. Christ in us will bring them to God, we're just the worm who dies at the end of the fishing line being cast into the depths of the sea to bring them onto dry land.
God is love, and if his love is in our hearts then we'll care for everyone and have the hope in our hearts that they will enter into heaven our job is to bring God to others and he'll do the rest. I was thinking about the tree, once we plant it, God in his time with water and light, causes the tree to grow. And I thought of how Adam and Eve used leaves to cover themselves. These leaves would have been taken from the tree, but they wouldn't have been growing on it anymore. And this is like covering ourselves in the word of God, like reading from the Bible but it's not growing within our own hearts. God will cover us if a have faith and obey him. If we try to cover ourselves, God will see our nakedness even if man can't, we can't hide our sins from God, we should repent and turn away from sin.
James 1
But every man is tempted, when he is drawn away of his own lust, and enticed. Then when lust hath conceived, it bringeth forth sin: and sin, when it is finished, bringeth forth death...
Once we know God, we should turn from sin to remain in the light God and not turn to darkness again, remain unspotted from the world being led by the spirit and worship God in spirit and in truth following Jesus.
1 Peter 2
But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar people; that ye should shew forth, the praises of him who hath called you out of darkness into his marvellous light: Which in time past were not a people, but are now the people of God: which had not obtained mercy, but now have obtained mercy.
Dearly beloved, I beseech you as strangers and pilgrims, abstain from fleshly lusts, which war against the soul; Having your conversation honest among the Gentiles: that, whereas they speak against you as evildoers, they may by your good works, which they shall behold, glorify God in the day of visitation.
