Take it one day at a time. The entire process can seem daunting. Break it down into small steps and take a deep breath. I would get yourself into individual counseling. Hugs and welcome.
You and your son deserve more than that. Get yourself to therapy ASAP, it will help you gain courage to move on. Don't be afraid of telling people IRL. Most friends and family will likely be supportive. And it's your life, who cares what they think!? Your happiness is number one.
Also the thought of telling anyone IRL is terrifying.
You don't have to tell anyone yet if you're not comfortable. Me, I needed the emotional support of my parents and I knew beforehand that they would provide it and help me, but it was still one of the hardest things I had to do. Once I told them, then it got a little easier to say it the next time, and the next...now I can say it without crying, but I don't know when I'll be able to say it without some grief.
Stay strong - seek out a good counselor, and get the advice of your lawyer. Document everything if you can - emails, bills for online dating websites, browser history, etc. especially if you live in a state where you can use adultery in your case. Make an escape plan so that you and your son will be protected physically and financially.
It might be scary to leave. But it's scary also to think of your life continuing on this path. And not just yours, but your sons too. Is that the example you want to set for him and how he should treat his future partner?