I lied to my SO and cheated.

Lately my SO has been down about his weight. He's had no motivation whatsoever to do anything about it. I told him we could diet and work out together and both get in shape. However, I am perfectly happy with my body and so is he. I CHEATED: I had a girls day with his sister and we went to lunch. I went nuts on the dessert bar and ate a lot of junk food! With the dieting lately my stomach wasn't used to it and I came home miserable and sick. I LIED: I knew why I was sick and he asked me what was wrong. I told him I must just be getting sick. I feel horrible. But I feel like I got my karma Lol. Should I tell him, and let him have a cheat day, or keep my mouth shut and keep him motivated,and on track? Idk how women cheat on their spouses, I can't even cheat on a diet without a guilty conscience! Advice please?!