Resenting someone can be a taxing thing. Without addressing issues in the past, we are continuing to tax our present and future interactions. If you haven’t found the strength to tell your loved one how they have hurt you then maybe your complaint isn’t as justified as you believe it to be.
This negative toxicity needs to be removed as quickly as possible whether it is you notifying the person that you have resentment towards or you talking yourself out of resentment. There is no reason to give negative emotions harbored from the past the power to cause further negative consequences in the present and future.
Dig that resentment out. Cleanse the toxins. Have the subjectivity to observe the toxicity of resentment in yourself and the diplomacy to communicate it to another. Only then will the growing negative energy of the present become a dying memory from the past.