I feel really bad

I have a girlfriend and i love her more than anything, i literally only have eyes for her. Well today at work my female manager was talking about her dyed hair and i said “it looks good”. I don’t even know why i said that, its unlike me to give any other females compliments besides my girlfriend and i feel dirty, i feel like shit. I have absolutely no interest in my manager or any other girl than my girlfriend. The guilt is killing me right now, should i tell my girlfriend what happened? I feel really bad and i want to tell her.