STOP! However much you have had your heart hurt... just stop! STOP! Because me and a million other mother fuckers had it worse than this. I remember how pathetic I felt. That's why I am going to give you the best information on how to deal with this. I logged each day when my heart was ripped out and pissed on (don't do that, it doesn't help you get through it faster) for lucky fuckers like you who get to reap the benefits of it.
We have all gone through this. It's a part of relationships that you need to accept. Those who haven't yet still have, their girl just hid it well. Being in LTR's are a gamble. It's a risk. It's troublesome. And probably exactly why you came to this forum. This is why for right now, you come first in all this. How can one take care of them self after this happens? You don't know how. Your mom won't tell you. A therapist will burn your ass for money and make you rehash your entire existence in the process. But no fear I am here.
At this point, my advice is going to directly reflect what you really need right now. That is some you time. Maybe you have been letting it sink in the past 5 weeks... but how much has it sank in? You got fucked and left for dead. Repeat that to yourself and learn to accept it.
Here is the advice. Take it or leave it.
Temporarily remove yourself from the social circle that brought this chick around with her new boyfriend. Venture out and find some new friends. But, for right now is that even what you truly need? Ask yourself. Maybe you need to sulk in your bedroom for a week because these feelings were just brought back to the surface. Let the dishes pile up on your bedroom floor and be sad. Sleep a lot. The whole weekend. Stop pretending you're okay and be heartbroken with yourself for a minute. Digest what happened. Fucking cry bro. So what? Call that unmanly if you'd like. Maybe it is, maybe it isn't. But regardless, this is the learning portion for you. From here forward you can develop yourself into a man that this will never happen to again. A stronger person. You won't allow yourself to be crushed like this because the next chick won't be capable of it. For right now. Learn from this forum. See your mistakes that you made, and fix them. Up the ante and challenge yourself to take nothing but positive things from this heartbreak going forward.
You don't need to speak to her ever again. That's preference. In my case, I nexted and never looked back. You'll probably do the same. Took me a couple months to digest that feeling. But it comes. Now as for the clearing your head portion. AHHH that is the real mysterious thing no one ever tells you how to actually deal with. Why is that? Well for one, your friends shouldn't just be talking to you about this. They should have knowledge like this: (that's what TRP is for I suppose, making up for friends shortcommings)
Let me break this down quick and easy for you.
Love is an addiction. We want it to stay there and be available for us when we get it. So, when your brain releases dopamine, which is a "feel good" chemical, some pretty shitty things start to happen. Once the chemical is released, the brain quickly looks to its memories and realizes that this person is gone. This thing you're craving. Then all at once a storm of sadness and anger and so on and so forth come crashing in. Memories of hurt. Memories of once upon a time happiness. This may cause issues with your bowels and tightening in your chest (AKA a broken heart). These things are occurring due to evolutionary factors. Our brain is trying to show us that what happened to us isn't cool. And next time your ass better be a much better judge of character and more observant to the world around you because that bitch sucked the life out of you and you let her.
Now, lastly. Breath. Take it easy. She wasn't a unicorn. She wasn't supportive when you weren't at your peak. Let it be. Instead of lashing out and raging in your mind, learn acceptance. Repeat to yourself that you accept what has occurred and you are making changes to protect yourself and feel better. Whatever has been stripped from you, you will get back. You will be on top again. Relax and remember these things.
Starting tonight, listen to self hypnosis (completely sober) every night before bed for the next X weeks. I suggest Michael Sealey on youtube. In particular, I would start with the "letting go of past relationships" video. Then move on to the confidence section. Make sure you stay up all the way through the video and don't fall asleep until after it is done. Promise, you will feel so much different after.
Calm your mind first. Break the habit of the obsessive thoughts next. Then rebuild yourself. Lastly, identify who you are and what you want when you're completely over this.
You will get there. This will be nothing to you shortly. Have faith in the process. For now stay completely away from her, maybe even indefinitely.