Good advice so far.
I will re-stress this point: Once a woman loses attraction for you, it cannot be undone. It is simply the way women work. Her loss of attraction was not overnight and by the time she dumped you, she had been wanting to do it for a long time and got to the point where she literally couldn't stand it anymore. In RARE occasions, you might still be able to get an ex back, despite her loss of attraction, but it will never be the same, it won't last very long, and she will dump you a second time. This is true for 98% of all cases. Do not think you are going to be in the 2%. We have all been through this. Best to focus on moving on.
Re-frame your relationship with her: She was not here to be your long-term partner or your wife. She was here to give you the gift of self discovery.... she was here to cause you to find red pill and this forum, and to work on yourself to become a better person. To get rid of your neediness, insecurity, and immaturity. Each woman we date is here to give us a gift and she gave you a major one.
Men's brains are biologically wired to solve problems. It is how we have survived as a human race. A woman dumping us presents a huge problem for us because we want her, even more than ever before, and our brains go into overdrive trying to "solve" it. Emotions take over and we spiral. The first step in moving forward is discovering you have a different problem to solve: Fixing yourself. You've discovered that already so congratulations. And you've discovered this site. The second step is accepting the fact that you'll never get her back. That may take a long time, but as you learn the mindset shifts, and as you learn to have abundance with women, you will look back on this girl and laugh at how highly you valued her. You will be dating increasing amounts of women and they will get hotter and hotter until one day you stop and think to yourself, "I never would have dreamed I'd be sleeping with and dating girls this hot. I can't believe how obsessed I was with my first girlfriend!"
As for books/channels, you can read the DJ Bible and Book of Pook here for free. On Youtube, I recommend Corey Wayne for newcomers. He has a lot of videos, explains things well, and covers all the basics you need for starting out. Start by searching for him with "needy" and "insecure" etc and then browse through the rest of his videos and pick which ones seem interesting. Just be careful of his breakup advice videos - he does suggest that you can change yourself and *possibly* get a girl back but I disagree with him on that... though he does admit that it doesn't usually work and you need to focus on yourself instead, so that when another good woman comes along, you'll be ready. He has a book you can get for free as well. I don't agree with 100% of his advice but the majority of it is a solid foundation to start out with and you can modify it with your own learnings and experience as you try out the advice he gives, and the advice you get here.
It took me a year to make meaningful change. Three years to completely transform my dating life.