May I ask if you use any spanking methods ?
ur sayn that u hav never left ur son with him?! is he means to ur son when ur around?
Is your son ever alone with him ?
I think you need to figure out where your son got the idea that any kids get "whipped", and why he is saying your 2nd boyfriend is doing that to him. My 4 year olds would have no idea - none whatsoever - what being "whipped" meant. You need to find out why your son, who you believe is completely protected by you - knows what that means.