I messed up bad, need help

Okay, so I need to get this off my chest. I messed up. Really, really bad. I cheated on my wife. Her name is Sarah, and we've been together for like, ten years. I don't even know why I did it. It wasn't even good. It was some stupid one-night stand on a business trip. I came home, and I just felt… dirty.

I haven't told her. I can't. I'm so scared of losing her. She's my best friend, my everything. We've built a life together. We have a dog, a house... plans for the future. Kids, eventually. How could I throw all that away for five minutes of… nothing?

But the guilt is eating me alive. I can't sleep. I barely eat. I'm snappy with her all the time, and she's noticed something is wrong. She keeps asking me what's going on, and I just lie. I hate lying to her. It's making things worse, I know. I feel like a total piece of garbage.

I thought about telling her. I really did. But then I imagine the look on her face, the pain in her eyes... and I just can't do it. Maybe if I just keep it buried, it will go away? But I know that's not true. It's just going to fester and rot until it destroys us both.

What should I do? Should I confess and risk losing her? Or should I keep it a secret and live with the guilt for the rest of my life? I honestly don't know what the right answer is. I feel so lost and alone. I need some guidance. Any advice would be appreciated.