G.W.
I would be concerned if he was truly terrified and did not want to be with a specific person. I would call it a phase. You may need to start preparing him for transitions in advance - - "We are getting ready for school, let's name all of your friends, the fun things you will do, what we will do when I pick you up" etc. Count your blessings that he does now meet a stranger - you want him to be careful. I recommend the John Walsh video - Safe Side (I think), when you are ready for him to learn about stranger danger - it gets the message across but is funny.
Anyway, back to the issue, on the whining, we have a rule in our house that when you whine, the answer is no. You must use your nice voice and good manners to be heard and understood. Be consistent and stick to it, or the whining never ends - I have seen it and it is not pretty. ( :
Good luck!!!