These thoughts and need second opinion

Today had fear about cheating to​​ my girlfriend. We ​talked previously about exercisihg together but she said she would cook. But agreed that we can exercise. Thought she then agrees on exercising only because of me. And said no and went in the other room and seconds before this thought that if it were the make colleague he would agree. I feel bad because of this thought it feels like cheating. I felt some madness in myself while going in the other room. Now I feel sorry, it's been several hours. I feel bad because I even stood up and went in the other room and this is a physical action.