cheating: what is your definition?

. So my bf tells me about a strange girl calling asking if he wanted head, of course I asked a million questions to make sure he played no wrong role, at the end I asked him his definition of 'cheating' and he said having feelings or doing anything sexual including kissing 🤔. As a female what do you consider is 'cheating' because his response seemed to be a little too common sense almost and I don't want to think it's just me ... .