Physical for me would be kissing or touching with the intention of intimacy, everything from that point
Flirting is not cheating in my book nor my SO's book
Emotional cheating would be only if my SO hides it from me, if he feels attracted to someone else I believe it is his obligation (as far as being part of a committed relationship) to tell his current partner, either they decide to work it out or go separate paths is other topic, but hiding that feeling for someone else from your SO is heating for me.
Not in an open relationship, but if he ever decided to go a different path I would totally understand it, just be honest about it, if you're not, then you are cheating