BE GLAD TO SEE THE BACK OF means that you are happy someone or something unpleasant is finished or gone.

For Example:

Last night we had a farewell party for John, but to be honest I’m glad to see the back of him. (Meaning I’m glad he is gone).

Christmas came and went and Ruth was glad to see the back of it. (Meaning Ruth was glad Christmas was over).

Far from being glad to see the back of Kylie as some reports had suggested, there was sadness over her departure.