"My dog is really clingy at home, he follows me everywhere"
Your dog is a social animal, which means that he seeks proximity to the individuals who are in the same home, with whom he feels trust and safety. Following you everywhere indicates his interest in your presence and your activities. In no way does this predict that he has or will have separation anxiety. Boby, my dog/friend when I was a teenager, was likely to follow me in every rooms, yes, e-ve-ry. And yet, when I left for school or somewhere else, he could stay serenely on his own.
"My dog is independent at home"
The fact that your dog is able to be autonomous at home or that he does not follow you everywhere does not indicate that he does not know where you are. The hearing abilities of dogs allow them to fully locate you in an environment, even without being near you. Your dog may appreciate your presence, your company nearby, without necessarily being a big fan of interactions. That being said, it is important to distinguish between not interacting and feeling lonely.
"I give my dog ​​attention, so he has separation anxiety"
You can play, cuddle, pet, teach tricks to your dog, speak to him constantly, sleep with him, watch television with him on your lap, and yet he would not suffer from separation anxiety.
You could have an aloof relationship, you and your dog could be essentially room-mates, and yet he would suffer from separation anxiety.
Several cases have allowed to determine that the cause is undetermined. It is supposed to be genetic. What is certain is that dogs who were socialized, familiarized, coming from the same litter, can be free from it, apart one. What you exchange with your dog is quality time. That can be soothing as well for him. If he shows he stresses out when you are leaving, and, you are stressed as well, he may be reacting to your stress, not to a possible separation anxiety.
"I won't comfort him"
It is important to keep it in mind that the behaviors expressed by your dog reveal a state of panic. Neither a whim nor revenge. Some anxiety has settled in him when he sees you getting ready, which means that his organism reacts as if your preparation to leave the place and leave him alone had the same value of danger as a lion opening his mouth on his throat. Then he is then not able to measure that the situation does not actually represent a danger for him. Reassuring him can calm him down. He cannot learn to cry in order to get you return more quickly to this context to play after; he can learn that crying puts an end to his ordeal more quickly and that he can then let his negative stress go.