why stability of halides decreases down the group?

As we move from top to bottom down the group , size of surrounding atoms i.e. halogens increases along with decrease in electronegativity . Hence due to large size H in hallides can be easily removed as it is not strongly bonded  . Whereas in case of HF fluorine due to its high electronegativity & small size is able to hold hydrogen atom strongly & thus stability of HF increases whereas down the bottom it decreases due to weak bonding.