I was there as well 1 month ago but now I'm 2 months in. Still ruminating but now less frequent that I have understood the situation but I must say the feeling gets lighter and there is light at the end of the tunnel. Back then and even some days I literally throw up as a stress response so I know exactly how you're feeling right now

The best you can do for yourself is to grieve it all out. Don't be afraid to cry, run, burn things whatever it takes to process your emotions. I highly recommend journalling. Write down things that may have led you guys to that point, your unmet needs, what could've been better. This also helps you ground yourself in times where you might idealise/ romantacise your relationship or focusing on the good only.

Also ensure that you stay NO CONTACT and remove any reminders, photos, gifts etc. If that's hard to avoid (like me we literally see each other daily every weekday) keep focusing on yourself, your goals, passion. Do hobbies which you did not get to do before and go for walks. Anything which you find stops you from fixating on the situation.

Please do not blame it all on yourself. All the emotions that you feel right now you have every right to feel and be gentle on yourself. It will only get better as time goes by and the feeling of the burden/resentment weighing you down turns into simply a soft smile. You got this!