$ sed -[eE] '/<RegEx>/{N;d;}' # removes the matching lines and the next line
$ sed -[eE] '/<RegEx>/{N;s/\n.*//;}' # removes the next line after the matching
$ sed -n -[eE] '/<RegEx>/{s/.*//;x;d;};x;p;${x;p;}' | sed '/^$/d' # removes the matching lines and the previouse line
$ sed -n -[eE] '/<RegEx>/{x;d;};1h;1!{x;p;};${x;p;}' # removes only the previouse line of the mathing