I think it's about to lose a person you really cared about, in this case a lover,
because the other person is just moving forward to other things so he or she is leaving his/her significant other behind, so now their relationship is lost, there's no reason for them to stay together, because they've changed, they are not the same so the things that used to keep them together not longer exist,
and about the golden cage, I think like it's golden because it is everything she or he ever wanted but it's a cage because the consequence of getting it was to lose a significant other.
I think it's about to lose a person you really cared about, in this case a lover, because the other person is just moving forward to other things so he or she is leaving his/her significant other behind, so now their relationship is lost, there's no reason for them to stay together, because they've changed, they are not the same so the things that used to keep them together not longer exist, and about the golden cage, I think like it's golden because it is everything she or he ever wanted but it's a cage because the consequence of getting it was to lose a significant other.