Please I'll like to hear ur view on dis question.
A Person that gives his life to christ and later turn to sin, Is he an unbeliever?

No! He's a backslider. He's still conscious of the existence of God and believes in Him. But he's finding it hard to separate himself from the things of this world.

Except if of course, he denounces Christ as his Lord.

Yasher:
No! He's a backslider. He's still conscious of the existence of God and believes in Him. But he's finding it hard to separate himself from the things of this world.

Except if of course, he denounces Christ as his Lord.

Is d spirit of d Lord still dwelling in him in that sinful nature

radiorebel:

Is d spirit of d Lord still dwelling in him in that sinful nature

It depends on the grace of the person, for example, when David sinned, he prayed that GOD should not take His Holy Spirit away from him, he prayed for forgiveness. Also, the group of brethrens Christ was referring to in Matt 7:22 fall under this category too. They would do great works in His name, but yet, workers of iniquity. This is the reason why the word of GOD said we should grieve not the Holy Spirit which dwell in us by sinning.

For some others, after sinning, the Holy Spirit leaves them till they reconcile with GOD.

But in all these, one thing stands out, no matter our works or what we do or who we are, if we die a sinner without repenting, hell is the destination for such soul. That is why JESUS urge us to watch and pray and hold fast to our salvation coz we dunno when we'll die or when he'll come.
Sin is very dangerous, the soul that sinneth shalt die