I had protected sex with my boyfriend during a possible herpes prodromal stage what is the possibility that i gave it to him if it was prodromal symp?

Herpes: you likely were shedding virus in the prodromal phase. Since you were using protection it is less likely that he was infected but there is still a chance. It would be wise if he does not know of the possibility to inform him. You also can shed virus without lesions. Talk to your doctor about antivirals to keep breakouts and viral shedding to a minimum.