When i go to my.knees to his.****.
When you took my hand and held it tight between your legs as I nibbled on your ear. Yes, I do believe that's when it went from flirting to something more than flirting - although I wouldn't call that sex .. :)
When you have sex
I ignored it saying it was just me being silly until they told me they were getting married...Never trust a friend as far as you can throw them...in matters of the heart.
I would say that when he's got his hand in your knickers... there was some point where it stopped being "just flirting".
different ppl have different threshold regarding that , so its difficult to tell in general ....nice question