I don't understand, where I come from flirting isn't cheating, unless your intent is actually get with these other guys.

Given that why do you need to tell him, why make drama out of nothing . If your conscience is bothering you, stop doing it and move on.

If your intent behind flirting is to find someone else. End it with him and move on.
This is just my opinion of course.
All the best.

( in case your unclear implying to someone your interested just in case your actual relationship crashes and burns is just 'using'.
I really hope you can find enough confidence and strength to not be afraid of being on your own.)