After your initial breakup, you go through a whirl wind of emotions and the first is a denial stage thinking that your ex was just angry and made a mistake and will call you any moment to apologize and you will get back together again.
Then after a couple of weeks depending on you as every person as every person is different in the way and time they take to process their emotions, you start to realize that they are not going to call or come back to you so you rehearse over and over of what you should have said to them.
Then the feeling takes over of your whole world is crashing down and is being turned inside out, your heart is being ripped out of your chest by some demon and you are flooded with these different emotions all at once and have no idea how to deal with them.
You cannot listen to music or watch movies because every song or movie whether it's about a breakup or love it makes you think of your ex partner, which makes you cry and cry. You lose your appetite for a while because eating makes you sick to your stomach and reminds you of all the meals you shared together.
Then you feel really, really depressed, they don't care anymore, you ask yourself did they ever care for you at all? You feel that life is not worth living without them and all you want to do is crawl into bed and stay there forever feeling sorry for yourself.
You start to fear that you are going to be alone for the rest of your life and Then you start Binge eating especially junk food for comfort and you don't care if you pick up some weight because if your partner didn't care why would anyone else?
Your mind starts racing at full speed ahead as you think non-stop about why they REALLY left you, asking yourself if they were being truthful when they told you their reasons, if it, didn't have anything to do with an affair, you start thinking the worst of them, putting all the blame on them and you become very, very angry with them.
Then obsession stage kicks in and you start calling your ex several times a day to check up on how they are doing and what they are doing. You are secretly hoping that they are as miserable as you are.
That doesn't work because they start ignoring your calls, so you start texting and emailing them constantly. You spy on them and bombard mutual friends with questions about them.
Then after a while you start to calm down slightly as it hurts a little less and less every day that passes by.
Not everybody is the same and we all go through these emotional stages differently but all the above are absolutely natural and common to feel, so don't feel guilty about your feelings. But if you are trying to get your ex back, the obsessive calling, texting and bombarding their friends will make him run the other way, never to be heard from again.