Don't want to hijack other threads so -
I'm atheist and don't believe in "sin". I do know a few people who steal, lie but I don't and with one notable exception, I don't count criminals among my friends.
There was a fundie here who was always preaching at me and others and repeatedly told me that even though I live a life of doing good deeds, harming no one, working to leave the planet a better place for having been here, I am "wicked" and would "burn for all eternity".
"Christians" say things like "I sin all the time", "I'm a sinner and pray to be forgiven for my sins" but what in the world are these sins that christians pray about? And instead of all this praying, why not just clean up your behavior?
It's a well-kept secret, hiding in plain sight: Jesus came to take away the sins of the world. Also in scripture: Non-believers will be judged by their own hearts. God, whether you believe or not, has imprinted right and wrong on the human heart. You, obviously, are following your heart.
We are also taught that God is love, and that He loves and cares for human souls. That includes you. You do not believe in God, and this is a far different thing from believing in God and rejecting Him all the same.
In many ways, non-belief in God seems to be a choice. In making this choice not to believe there is loss, but it occurs in the here and now. Your loss is very personal and it consists of not being able to know and love God in this life.
There is a parable you may like. A father had two sons. He asked both to go out and work in his vineyard. The first (let's call them Christians) said, "Yes, on my way," but never went. The second (let's call them Atheists) said, "No, I will not!" Later, he decided working in the vineyard was the right thing to do, and went out and worked.
If you are doing what your heart calls you to do, then my belief is that you are close to God, whether you realize it or not. You love His ways, even though you do not know Him. You are far from the person who knows God and His will--and deliberately rejects Him. Just want you to know it is possible to be even closer to God in this life than you are--and that there are many blessings there (if you like that sort of thing).