Dont think too much on this, if you think your manager isnt mature enough to handle 1 resignation then says alot about him as a person and leader. I wouldn’t want to work with him in future. But if he is a veteran and has seen people going then it wont impact your relationship with him. So no matter how say it, if he wants to take it personally its on him and if not then you are good.
PS - if there is a firing going on then do not give a moment of thought before switching if the offer is good. Its good to see you are thinking about the team but remember nobody is irreplaceable.