Part of what's helped me let go of issues is realizing that sometimes, people don't think like I do. And that I can't keep trying to convince them to see things my way. That my version of what's logical and how they see the world are two different things and I'm just spinning my wheels.
I'm the kind of person who likes to solve a problem if there is one. I don't like to just complain about it, rather I want to find a solution and work towards that solution.
But when there's someone you're close to in your life who treats you poorly, you want to make them realize that what they're doing is hurtful, hoping they'll stop doing it. And sometimes that's fruitless. You can try a million times and never get through.
As a child, I didn't have the option to just walk away from a toxic environment. I was dependent upon the adults in my life. It was my responsibility to keep everyone around me as happy as possible because if they were in a foul mood, they'd treat me horribly. I internalized this and learned that it was my responsibility to be the happiness fairy, always reacting to everyone's subtle behaviors and accommodating them and making sure they were as happy as could be. This was a lot of work, but then I was rewarded by not being berated or being treated as poorly.
Sadly, since this is what worked for me as a child, I never questioned it and I continued to behave that way as an adult. Always being too accommodating and always internalizing things. If someone was unhappy, I thought it was my fault, and therefore, my responsibility to fix. If someone, anyone - a friend, relative or a complete stranger - criticized me, they must be right and it was my responsibility to fix.
My self-image was dependent upon how others viewed me. So unless I had 100% of the people around me telling me I was wonderful, then there was a problem, and it was my responsibility to fix it. Now, I try to tell myself that the most important opinion is my own. As long as *I* think I'm honest, nice, fair, generous, etc, it is less important that someone else think so.
Several things have helped me to stop ruminating over things. One is that I ask myself "If the tables were turned, how would I have acted?" Would I have been as entitled, thinking that I had a right to do X, as they did? Would I have been rude and screamed like they did? When I realize that I would not have behaved as they did, I realize that we are different. And that I can't reason with someone who just doesn't think like I do. That eventually, I have to give up and stop trying to make them see my reality. Once I realized that I couldn't fix things, it was helpful to learn that sometimes the only solution is avoidance. Sometimes, the only way to win the game is to not play at all. Put your cards on the table and walk away. Stop fighting in the tug of war, drop the rope and walk away.
A good piece of advice I got years ago was that you can't have no thoughts. Your brain is always thinking of something. So if you want to get rid of a thought, you have to replace it with another. If you're always ruminating over someone or a situation, you can't just say "Stop thinking about it." You have to find another more pleasant topic and try to get yourself to think of that instead.
I read a book called "The Brain that Changes Itself" and it talks about how certain pathways in the brain are well-worn. Kind of like a rut in a road. If you keep taking that path and thinking about that thing, the brain tends to take that path more easily the next time and the next until it's almost automatic. If you want to take a new path, the first few times, you have to fight with your thought-process, like moving the car tires and pointing them down another path. You have to say "I am not going to think of A, I will think of B instead" and go down a less-worn path. Each time you find yourself going down the old path A, you move and try to go down path B or path C. Eventually, path A is not the automatic path and you don't think of it as much anymore.