How can I stop thinking about him/her? Why my heart hurts so much?

Try thinking about things that you like to do! It really helped me when I went through a rough breakup, just try to keep yourself occupied to keep your mind off of them.

Try to do something like a hobby, get your mind of the sadness, like hang out with friends go swimming etc

Because you are in love. I have experienced the same thing. Maybe you're hurting because of some negative thoughts. Love is an unpredictable feeling

I have always tried diverting my mind to something else... for me that is guitar and music, it makes me feel like im free

Emotions versus reasoning are torn into two. Find a reason to think about one's well-being. Try to apply those emotions to focusing on yourself and taking what you think is in ruins into something positive and constructive. It's easier said than done, like witnessing a collapsing old building and building a new, better skyscraper to replace, metaphorically. Seek friends and family, who truly care about you. Spend time enjoying their company to distract yourself from thinking about the past. You are never truly alone to fend off your own demoning thoughts. Eventually, the void in your heart will fill by the accomplishments you've done (for yourself and others) and the ones who got to share witness of your rise.

I have found that it helps if you focus your mind on other productive tasks. Perhaps, reading a book or taking a walk. Listing some hobbies you enjoy and selecting the one you feel will help most is a good option. Don't worry, it will get better in time.

Try to busy yourself, surround yourself in people you love like friends or family. If it's difficult to focus one more than one thing, fine something you really enjoy and dedicate yourself to it 100%, sit and listen to music, watch movies or videos. Play games even! never sit and dwell, it'll always just make you more sad and upset.

The pain didn't leave your body. You still care about them. Even if you don't want to but you do. Every time you think about them makes you wonder what happened

Look for distractions. It can be exercising, or simply doing something you love; reading, swimming, cooking.

Occupy yourself with your favorite hobbies and focus you and what you need right now . make peace with him/her, try to understand why it ended. Really think about him you felt for that person. Think am I happy ? Is that person happy? Are we really good for each other? And when you really think about it and realize that either you and that person are just better off without each other and its both what you want thenotherjust let go.