I Messed Up Badly

Okay, so, I'm married. Happily, I thought. But this coworker... we just clicked. Lots of late nights at the office, talking. Then, drinks after work. It happened. One night. I slept with him. It was awful. Not the sex, but the feeling after. Like I'd ripped a hole in my life. I haven't told my husband. I can't. I love him so much. But now I feel like I'm living a lie, and I don't know what to do. I'm so, so guilty. I hate myself a little right now. I just needed to tell someone, even if it's just anonymous on the internet. Please don't judge me too harshly.