Can a human ever be happy in the afterlife while not loving God?

I think that the best way to look at happiness is as God's 'rays of light'. If you hide from them you won't recieve their warmpth. It's up to the individual as to whether they hide or not. I believe, like in CS Lewis's The Great Divorse, man will be offered the hand of redemption regardless of their past or previous blindness to truth. Those that shall remain outside the heat and love of God's rays are those that will truly decide that they despise His glory and prefer to go their own way, even if that way is true death (He offers true personality and pleasure).

Of course, this is all guess work. But God IS love, joy and forgivness...What He isn't is despicable. Or (probably. Most probably) an old man with a beard.

We as Christians are generally not as convinced of our virtue as atheist are.

Some pertinent bible verses

<< John 3 >> New International Version 1984

Jesus Teaches Nicodemus

1Now there was a man of the Pharisees named Nicodemus, a member of the Jewish ruling council. 2He came to Jesus at night and said, “Rabbi, we know you are a teacher who has come from God. For no one could perform the miraculous signs you are doing if God were not with him.”

3In reply Jesus declared, “I tell you the truth, no one can see the kingdom of God unless he is born again.a”

4“How can a man be born when he is old?” Nicodemus asked. “Surely he cannot enter a second time into his mother’s womb to be born!”

5Jesus answered, “I tell you the truth, no one can enter the kingdom of God unless he is born of water and the Spirit. 6Flesh gives birth to flesh, but the Spiritb gives birth to spirit. 7You should not be surprised at my saying, ‘Youc must be born again.’ 8The wind blows wherever it pleases. You hear its sound, but you cannot tell where it comes from or where it is going. So it is with everyone born of the Spirit.”

9“How can this be?” Nicodemus asked.

10“You are Israel’s teacher,” said Jesus, “and do you not understand these things? 11I tell you the truth, we speak of what we know, and we testify to what we have seen, but still you people do not accept our testimony. 12I have spoken to you of earthly things and you do not believe; how then will you believe if I speak of heavenly things? 13No one has ever gone into heaven except the one who came from heaven—the Son of Man.d 14Just as Moses lifted up the snake in the desert, so the Son of Man must be lifted up, 15that everyone who believes in him may have eternal life.e

16“For God so loved the world that he gave his one and only Son,f that whoever believes in him shall not perish but have eternal life. 17For God did not send his Son into the world to condemn the world, but to save the world through him. 18Whoever believes in him is not condemned, but whoever does not believe stands condemned already because he has not believed in the name of God’s one and only Son.g 19This is the verdict: Light has come into the world, but men loved darkness instead of light because their deeds were evil. 20Everyone who does evil hates the light, and will not come into the light for fear that his deeds will be exposed. 21But whoever lives by the truth comes into the light, so that it may be seen plainly that what he has done has been done through God.”h

First of all, Christianity doesn't teach that some get to go to heaven because they are "smaller sinners" than everybody else. Likewise those in hell are not their because they are "bigger sinners" than anyone else. In fact as humans we all stand on pretty equal ground as far as that is concerned, and if that were the standard we'd all be in hell.

Secondly, men do not hate God because of the world he created, they hate God because he is good and they are not. However consciously or unconsciously, they hate him because he is altogether different than they are. They do not understand him and if they did they would not like what they found. The Bible teaches that men love darkness because their deeds are dark and that God is light. (John 3:16-20) Men will naturally hate that which brings judgement to their deeds. God created the earth "and it was good", there would have been no reason to hate it except for the evil deeds of men that have polluted it. A truly Christian perspective on "hating the world" would involve hating the pollution of sin in it and therefore hating ourselves which would turn us to loving God.

Another point that comes up in your question is the issue of choice. The Bible does not speak of any opportunity for new choices to be made after death. Even though everything will be laid bare and there will be no longer room for doubt or question, the choices are made here. They will be sealed there. Those who (through God's intervention in giving them a new heart) chose to hate sin and love God on earth will continue to do so and be truly happy in his presence. Those who have not been redeemed and hate him here will continue to do so for all eternity even though his nature is revealed.

And to bring all this round to the core of your question: No, it will not be possible for a human to be happy in the afterlife while not loving God. There is nothing else in heaven to be happy about. The lamb on the throne is the central theme in the description we are given of heaven. Heaven is heaven because God is there. It will be unquestionably happy for those there because they will love him (even more than they do now). For those apart from him there will be no happiness at all, only weeping and gnashing of teeth.