I have a few suggestions, if they are welcomed!

The second line may sound better as "The sorrow is too painful". The use of "much" here sounds clunky, but since you are making a comparison in the next line, maybe use "more" to work with "than", like:

"The sorrow is more painful
Than the scratches in your pride"

And then in the last line, "siped" should be "sipped".

I also wondered if at first I had misread "lack". It's an interesting use here, and one I don't see, since I usually associate "lack" with a deficiency or someone has a "lack of" something. It made me think if you are already losing faith and spirit, and this person perhaps was close to you, yet you both kept drifting apart.

My interpretation is that the poison is self-sabotage, or this wedge that keeps drawing the two of you further and further away. The despair, the hope that things will change in the relationship, the desire to have that sense of excitement and motivation back. It definitely made me think of how depression can convince us we're a "burden", when the opposite is true. And how we can cling on to hope, and what we once believed, hoping it can anchor us and make us steady again.

Keep writing!