Everyone belongs here if they have thoughts, questions, or feelings of polyamory.
I have two thoughts on your situation.
The first is that if your wife doesn't understand love, she most definitely will not understand polyamorous love. Polyamory requires the loving support of partners who want your happiness and are willing to do hard work on their beliefs and feelings in order to encourage your full potential of happiness.
The second is that adding another person to a broken relationship is just sucking them into your pain. You're absolutely right that it reaches a point where you have to save your own life, seek your own happiness. I don't feel that bringing someone else into your life to so-called "fill in the gaps of your marriage" will do that. I think it will bring to your life more pain and anguish than joy and happiness.
A lot of people don't know how to love. It's something we learn as children and is very difficult to learn later in life, although it can be done. Before looking for a new girlfriend, I would try marriage counselling to communicate that your needs are not being met and to see if there is the possibility within the relationship to meet those needs. If not, it may be necessary to admit that you need to leave the relationship in order to save your happiness.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker