I can only say from my own experience. I just said "thank you" for all the good things that we had together, for those gorgeous moments and memories that he gave me. I put a point and left. And never came back.
Do not cling to the bad that you had, then anger and strong resentment appears, but it must be worked through and it is not easy. The experience you received is already yours, and you can't get away from it, don't be angry at her or yourself, and just try not to repeat the same mistakes.
Give yourself time to be alone, be sure to keep yourself occupied anything. Maybe just take care of yourself or pull up those things on which you may have put the "cover". I always propose to plan a small trip, if there is an opportunity, even to a neighboring city for a couple of days, a new place helps to clean up old emotions, or rather to move them and give place to new ones. Maybe go jogging or sign up for a couple of boxing classes, oh, how good it is to knock out all the bad emotions!
And the girls are all different and by no means all women are bitches and manipulators, and you perfectly understand this with your brain, just you still have pain and resentment against your ex.
Make the most of the experience gained in order to minimize risks in the future.
Your ex-girlfriend has done you a great service - invaluable experience and most importantly she herself confessed her sins. Now draw conclusions, analyze what happened, how she behaved when she cheated. Surely you guessed from time to time, but drove these thoughts away. Try to remember such moments so as not to get caught up in something like this in the future.
It's the same with manipulation, in fact, if you wish and if you are not blinded by love, these manipulations are easy to recognize. If not, then try reading psychological literature on the topic or contacting professionals.
I had a very similar problem and trust in girls (and in people in general) suffered a lot. At the beginning of a new serious relationship, there were difficulties. My mistrust was very annoying to my girlfriend, especially since it was completely groundless. Then I began to remember past experiences and each time I realized how stupid I looked. Well, the girl should be given her due, she endured my mistrust for a long time and tried to help me. Now everything is fine, we have been together for more than 4 years and there is no mistrust at all.
Yes, of course all people are different and it will not work to equate everyone according to one criterion, but there are common moments that give out constant lies and manipulations.
As for selfishness, again, use the experience gained. Now you know how it shouldn't be and you can spot something amiss early on.
The main thing is not to close yourself down and do not think that all girls lie and manipulate us (in fact, all people lie, try to manipulate others and are real selfish, the main thing is how far they go in this). Try, hang out with girls, try to learn to recognize lies and manipulation. And when you find your love, do not rush into the pool with your head and leave a little room for reason. Most likely, you will also be suspicious of her and this will cause some inconvenience, but try to explain to her the reason for this behavior and if you are dear to her, she will try to understand and help.
I hope I was somehow able to help you with my answer. I am not a psychologist or a relationship expert, but I was in your shoes and was able to handle it. Good luck!
You definitely need TIME ! If you look closely, your resentment will turn out to be nothing more than persistence in your own rightness and the wrongness of another..and where is this truth? The truth is, after all, everyone has their own.
Later, when calming comes after a breakup, a lot becomes clear!)
Now you are at the highest point of emotion - so you feel cheated. And now, just the moment when you SHOULD force yourself to make the only correct decision, in my opinion, of course: to leave her.