"I am going to have to", "I have to", and "I will have to"
"I have to see you sometime" means any time in the future, starting now. "No time like now" is a valid reply to that, suggesting the "sometime" to be very, very soon.
“I am going to have to see you sometime” puts an additional time delay during which you won't have to see that person - such time will come eventually, but the nearest future is exempt.
As for will/going to, I suggest previous answers distinguishing the two.