OP, IME, DC of your DS's age and parents think totally differently.
I understand that you are worried about your DS, will he fall over and hurt himself on the walk to the bus stop? What will happen if the bus doesn't turn up, will he walk all the way to school? 
What if he falls and breaks a bone? You want to be there for him, to be reassured that he has arrived and is safe. I totally understand that.
Unfortunately, most DC of your son's age will see it a lot like this;
'FGS, My mother doesn't even trust me to walk to the bus stop...all the kids at the bus stop will be taking the piss mickey out of me for months, calling me a baby, asking me where my mummy is today, my friends might not even want to stand next to me. I will be mortified!!
I'd rather fall over and break a bone, that would look far cooler to my friends so long as I don't cry lol
I will prove how capable I am by walking to school if the bus doesn't turn up, maybe then my mother will realise how ridiculous she is being.
She even asked me if I wanted to stop texting her, but it's just easier if I do, because if I say I don't want to anymore, she'll probably worry all day and then she'll get upset, and I have to come home to her being upset. I just can't win, because no matter what I say, it always comes down to the same thing...she is only trying to show she cares, I am fortunate not to know what it is like not to have someone who cares so much...well it doesn't feel like I'm fortunate sometimes.
Why can't my mum just save it for when we're indoors and no one is watching??
She just doesn't understand what it's like for me..all she cares about is how she feels!! Grrrrrr!!!'
I have a DS, and he has gone through this, and imo you never stop worrying about them.
DS has driven miles down steely icy one car wide country lanes this morning, compacted with thick ice, no gritting and ditches either side of the roads, to get to work. He is a relatively new driver. I would be apprehensive about walking across the road, let alone driving down desolate country lanes in it, but I am not sitting here wringing my hands. I have learnt to switch off to a certain extent. It is tough, it really is, but if you don't switch off, you will spend your whole life sitting in a state of anxious hand wringing, and believe me it doesn't end when they get to 18.
I know this sounds harsh, but you are suffering the most here OP. Believe me, your DS doesn't spend all day wringing his hands and worrying about you.
Also, just out of interest, do you text your DS your movements? And how would it make you feel if you felt you had to keep him informed, even when you might not want to, for the sake of a peaceful life? Quite possibly that is how your DS feels.
He is reaching an age where he craves more independence, and to trust him to a certain extent is a wonderful gift to impart on him.