had an affair after splitting up

so i recently broke up with my ex, been single for like a month now. yesterday at work i met this really hot doc in the hospital lounge. he was so charming and we just clicked. ended up going back to his place afterwards, it was great. kinda shocked myself actually. thinking about it though, i dont think its cool that i did this while our breakup stuff was still fresh. should i tell him? or is it already over and done with?