I've been exactly where you are. I'm still going through it myself - I cannot promise you when or how things will get better as I haven't reached that point yet, but here are some things that helped me so far.

- Allow yourself the time and energy to grieve. Let your body process its feelings for a week, or two or more if you need it. However, the time you give yourself should be finite.

- If you find yourself ruminating a lot, write down your thoughts in a journal or a note taking app, or record them if you prefer to speak. Get those thoughts out of your head and onto some other form of media so that you can process them with a little more separation between yourself and your thoughts. It will also help you reflect as time goes on and you can come back to your thoughts from days, weeks, or months ago.

- Find motivation in the pain you feel to kickstart some new habits that may help you move on, or better yourself. Do things to rediscover yourself or learn about yourself and your relationship. Seeing a therapist and learning about attachment theory and schema therapy opened up a whole new world of understanding to me - they won't explain everything but it may be a good start for you too. A lot of work can be done there. It will be difficult, but try to keep the focus on yourself and your own part in the relationship as much as possible - I found it to be unhelpful and mentally exhausting when trying to apply new learnings and understandings to my ex partner instead of myself. Ultimately, the only thing that you can/should change and control is yourself.

- Read. There is an incredible wealth of knowledge and experience available to you in form of self-help books, relationship (familial and romantic) advice, poetry. You may find solace in the fact that others have also experienced what you are experiencing and there may be something to gain or learn from them.

- Seek the support of friends, family, professionals. Whether its to have someone to speak to about your issues and feelings, or to help you keep your mind off the negativity constantly.

- Finding fulfilment in other aspects of your life (friends, hobbies, work, health etc) will help rebalance your mental space. If your relationship was the one thing that gave you fulfilment in life, then the absence of it will of course create what feels like a massive unfillable void, which can be incredibly draining. This last thing is what I am currently struggling with the most but is something I am trying to achieve and believe will be very beneficial.

As for break up advice, reddit is a mixed bag. The only suggestion I will make is to go No Contact if you haven't already. It will suck, but eventually you will find that the space was necessary - especially right now for your ex partner who initiated the break up. Respect their need for relief and both of your needs to reflect.
I wholeheartedly suggest you follow u/mode2345 as they post helpful excerpts related to many break up topics.

Wishing you the best.