"You freak me out" = "You scare me". These are in the simple present tense.
"You are freaking me out." = "You are scaring me." These are in the present progressive/continuous tense.
"Freak out" is a separable phrasal verb.
" freak out" is a slang, means " to lose or cause to lose emotional control from extreme excitement, shock, joy, fear, despair, etc.
" freaking" means " making sb frightened, nervous or wildly excited".
In the USA, you should use "out" - so either "freak out" or "freaking out." The only time I hear "freaking" is when it is used as a socially acceptable alternative to a certain profanity. However, if you said "I'm freaking" or "that freaks me" in the USA, people would understand what you are saying and would not think that you were using an idiom incorrectly or that you were uneducated. Either way should be fine.
In the USA, you should use "out" - so either "freak out" or "freaking out." The only time I hear "freaking" is when it is used as a socially acceptable alternative to a certain profanity. However, if you said "I'm freaking" or "that freaks me" in the USA, people would understand what you are saying and would not think that you were using an idiom incorrectly or that you were uneducated. Either way should be fine.