Passing non-temporary object to const string reference still prints garbage

I was trying to write an iterator by myself for my_vec:

#define BEGIN true
#define END false
#include <vector>
#include <iostream>

template<typename Container>
class my_vec {
private:
    class iterator {
        const my_vec *this_vec;
        using iterator_type = typename std::vector<std::pair<int, const Container&>>::const_iterator;
        iterator_type itr;
    public:
        iterator(const my_vec &s, bool state) :
                this_vec(&s) {
            if (state == BEGIN) {
                itr = s.v.begin();
            } else { /*(state==END)*/
                itr = s.v.end();
            }
        }
        iterator& operator++() {
            itr++;
            return *this;
        }
        std::pair<int, const Container&> operator*() const {
            return std::make_pair(1, this_vec->dog);
        }
        bool operator!=(iterator other) const {
            return itr != other.itr;
        }
    }
    ;
public:
    std::string dog = "DOG";
    std::vector<std::pair<int, Container>> v;
    my_vec(int space) {
        v.reserve(space);
    }
    iterator begin() const {
        return iterator(*this, BEGIN);
    }
    iterator end() const {
        return iterator(*this, END);
    }
}
;

However, when running the following main.cpp:

#include "my_vec.h"

int main() {
    my_vec<std::string> t(6);
    t.v.emplace_back(std::make_pair(1, "HELLO"));
    t.v.emplace_back(std::make_pair(2, "BYE"));
    t.v.emplace_back(std::make_pair(3, "CAT"));

    for (const auto &pair : t) {
        std::cout << pair.first << std::endl;
        std::cout << pair.second << std::endl;
    }
    return EXIT_SUCCESS;
}

The expected output is:

1
DOG
1
DOG
1
DOG

However, the actual output is:

1

and then the program stops or prints garbage.

It seems like the problem is in this function:

std::pair<int, const Container&> operator*() const {
            return std::make_pair(1, this_vec->dog);
        }

Why is this behavior happening as 'dog' is not a local variable?

Also, how can it be fixed without changing the function definition of operator*?