I understand the feeling of simmering resentment. I can only tell you what helps me; it may not be of help to you, but maybe it will.
I move on with my life if there doesn't seem to be any way to resolve or make situations better. This is not an easy task at all. I can feel very misanthropic, due to how difficult it is for me to get along with others. It is such a struggle, that it seems not to be worth the effort. I am going to try a different approach -- it may not work, but my current lifestyle isn't functional enough for me to keep trying.
I want to enjoy life and be productive, constructive, and be a positive influence. I can't do that if I am so miserable that it makes me hate everyone. It is up to me to find a lifestyle that will support my needs and wants. I've decided to try visiting another country for a while, and join a volunteer work program. I am learning a new language just to find out if I can find somewhere I fit in, or at least find a place I don't want to commit suicide/homicide, or both. I am a proactive problem solver, but sometimes situations are just too broken to continue to patch up. Similar to a leaky ship -- sometimes it is so damaged that you have to just scrap the whole thing and start over. Yep, it sucks, but the longer you wait, and keep trying the same things to fix conflicts, the more time you lose to a nonfunctional life.
Oh, that saying "sink or swim" fits in here I think. I choose to swim. I hope you do too.
I also hope you don't have a water phobia, or that idiom is an unfortunate choice for me to have used.