I am always baffled by the type of atheist who claims to accept science over religion, and yet claims there is no such thing as an "afterlife". According to science itself, in a way, there is. No energy can be created or destroyed, only borrowed. Every particle of your being will live on and be redistributed throughout the universe. It's a beautiful concept, and I find it more comforting than the idea of Heaven, personally. The soul- which is debated by some atheists in the first place, but let's just call it the "personality" in this example- is obviously not effected by the laws of physical science, but if atheists believes that the personality is made from your brain and your memories, then technically, according to the Law of Conservation of Matter and Energy, those parts that make up who you are continue to exist.
Knowing that my loved ones are simply becoming a part of something else, and that they themselves were comprised from billions of pieces of others who have come and gone, makes me feel that we are infinite.
Honestly, though, when it comes to religion, I believe that we are born alone, we live alone, and we die alone. Your world revolves around you, and your journey is only experienced by you. No one can know exactly what it's like to be who you are. I think that if you believe in Heaven and Hell, you are sent to one or the other according to how you interpreted your faith, and your god. If you believe in reincarnation, the same applies. And so on and so forth. I think if you believe in it, that's what happens to you in the end. If you ask 100 Christians of the same denomination to paint a picture of Heaven, you will see 100 different versions. I refuse to believe that any of the answers would be right or wrong, therefore I do not grieve differently when I lose someone close, because I know they are finding their own version of an afterlife, even if it is not the one I hope to find for myself.