Then it's a beautiful thing, my man. For the first time in a long time, you ARE in control of where you go. If Yahweh was real, then you were never in control of your destiny. It was all planned out since 6,000 years before you were born. One of the great logical paradoxes in Christianity. The whole "Free-Will" thing doesn't work if some super-being already knows how the movie ends.
Ditch the all-knowing sky daddy, and you've suddenly got yourself some gen-u-wine Free Will(tm)! Well, kinda. There's theories in Quantum Physics that say, basically, we're all just riding out the inevitable results of the Big Bang, like an infinitely complex set of cosmic dominoes operating on a sub-atomic level...
Personally, I don't buy into that theory, 'cos there's so much random chaos popping off all over the place at any given second, and the human thought process is a freakin' vortex of weirdness and unpredictability... But hey, even if it's true that we're just passengers on a cosmically pre-determined ride, we certainly can't tell the difference, so we might as well just roll with the punches and continue thinking we're calling the shots, right?
Anyway, whatever the case, it's a damn site better than thinking a malicious space wizard knows all about every little misery you're going to experience in life and in fact set it up that way as part of some unhinged "plan", all while being unbelievably cruel by telling everybody that they're free to make their own decisions.
I digress. Here's the best part - whatever good you do? Whatever you accomplish from here on out? It's lil' ol' YOU that makes it happen.
No strings attached. No puppetry. 100% you-ness, all day long.
That simple fact makes everything you do, positive, negative, neutral, whatever... It makes everything you do many times more significant. It doesn't take a god much effort to shove his divine hand up a doctor's ass to sock-puppet him into developing a cure for cancer. Different story if a simple man does it alone, without a magical assist from on high.
You have the capacity to do tremendous good for the world and for the people you care about; it's entirely possible you've BEEN doing good things for decades. But now hopefully you can allow yourself to take a little more credit for them, and maybe stand back and say "Hey, I'm a pretty good person. In fact, I kind of kick ass! I put a kid through COLLEGE! How awesome is that?" and smile for yourself. And it's alright to do that! You're not being vain, and you're not some damaged, broken, original-sin sinny sinner bad guy trying to make amends for silly superstitious crimes your ancient ancestors commited.
You're just you being you, and lil' ol' you single-handedly made the world a better place. For a few people, at least. I'm sure your kids are appreciative of the whole, you know, "life" thing.
Of course, the flip-side is that you need to man up and take responsiblity for your actions in all things, not just the good stuff. If you go around fucking up other people's happiness or doing damage to the world or even if you simply go life-passive and accomplish nothing noteworthy due to inaction. No demons or devils to blame, and no supernatural authority to forgive you and smooth your hair and tell you everything is okay. If you wrong somebody and want forgiveness, you actually have to go to the people you've wronged to get it.
Still, unless you're a sociopath or something, chances are you're a relatively decent dude on a human level, and you probably have the capacity to do a lot more net positive than negative, probably without too much effort as well... So, you know. Let the good times roll.