I think it means she is keeping to the promise of another-that they will be back again.
As the days grow longer she wishes more desperately for his return and grows sad and frustrated.
The singer says forget about him and when her hope dies for his return along with her love for him, then give into me. The singer has watched and would never forget her like this guy did. The guy probably regrets his memories of this girl he promised love and will forever feel guilty of leaving her all alone. What hurts this girl is that his presence still lingers with reminders of what they had so she could not forget.
I think it means she is keeping to the promise of another-that they will be back again. As the days grow longer she wishes more desperately for his return and grows sad and frustrated. The singer says forget about him and when her hope dies for his return along with her love for him, then give into me. The singer has watched and would never forget her like this guy did. The guy probably regrets his memories of this girl he promised love and will forever feel guilty of leaving her all alone. What hurts this girl is that his presence still lingers with reminders of what they had so she could not forget.