Less Enthused with Sweet Nothings

There was a substance,
inside of me that went unidentified.
For a while at least.
It was one I'd never experienced,
didn't know existed.
It was thick, slow, dark,
and it coursed through my veins at a crucial pace.
The substance,
it felt sort of empowering.
It completely consumed my heart,
which was once fulfilled with sweet nothings and essential bliss.
It approached my head,
and my mind was soon clouded, raided by this substance.
The mind where a betrayal replayed,
continuously.
... Although it had always been possible,
I had never thought true.
What is it about taking someone for granted? ...
By then sweet nothings were less enthused.
Bliss was overridden,
by the substance which had become my entire being.
I'd never felt it,
it was foreign.
It also seemed necessary,
and significantly justified.
Nobody forced me to feel it,
just allowed me to,
practically given me consent.
Now, the substance,
I have finally named.
The betrayal had triggered new found indignation -
I've been told it's called
resentment.