Why don't guys care when they break a heart?

Its not that guys don't care that they do. (and its not only guys that break hearts. Girls do it a lot also). But the way that guys and girls emotionally operate is completely different. I don't know what your situation was with previous guy/s. But you have to remember that we are simple creatures, and believe it or not we probably do not know what impact we really had on you.
but if it was a two way thing (where you both broke each others heart) then guys would generally close up which really does make it worse as it shows they don't care. BUT WE DO!

Its not that we don't care, its just that we really don't mean it!
but that's also the same for girls.

Don't generalize. Not all guys do this and just to let you know girls do it too. He obviously was not committed to his relationship with you. You were committed. He did the immature thing and he ran away. That is how some people deal with their feelings and emotions. When things get hard they turn their backs and walk away. He probably feels sad too but he just can't face you at the moment. That is why the songs says "Breaking up is hard to do"

Believe me, it isn't a 'guy' think. When things go sour one individual will always be left standing mending their heart because temporary love - not the real deal - is very seldom equal and one will love the other more and also hurt more when things are done.

In due time, once you heart mends itself, you'll be glad that this happened because now you are free to truly look for your one true love who'll never want to break your heart.

I don't think it's that guys don't care. I think guys just don't show their feelings as much as we women do. I'm sure he cares but why would he want to look vulnerable to you. Besides, how do you know he doesn't care? Did he watch you cry and and was he mean to you? Are you sure you're not just making a generalization here?

In this case I don't know if you call him telling him your depress about the break up or he dump you out of the blue without giving you a reason. But if there is a good reason why he dumped you maybe he just wanted to leave you alone so you can recover from this and learned to move on. However, if he just said its over then he is still immature not knowing how to face you the best way he can so he decide to just ignore it. Don't worry things will be okay after awhile.

Sweetie, when we are dating someone we always enter it believing he is the one, most of the time, they will not be the one, especially at your age. I know how much you are hurting but trust me, it will pass. One day you will wake up and realize the pain is a lot less until ultimately you will start seeing all the bad things in the relationship and how badly he hurt you and be grateful he is out of your life.

Guys that age are ESPECIALLY immature and they will often not show emotion, some date around and really not take things seriously. As you get older it changes but get ready...you will probably get your heart broken many more times and each time it hurts MORE, it gets harder because our feelings grow in intensity with age, experience and levels of relationships.

Try and keep busy, don't talk to him, stay away from him until you are healed. Seeing him, talking to him, trying to figure him out, get him back unsuccessfully will just deepen your pain and make it harder to move on.

Take a day to wallow...cry until you have no tears left, listen to sad break up music, talk to your best friend, write him a letter telling him how badly he hurt you and all your anger/pan towards (DON'T give it to him though, afterwards rip it up and throw it away, you'll feel better because you let it out), write in a journal, scream, throw things...whatever you need to do to vent and get it out. Then the next day start your life a new, begin the moving on process. Hope you feel better soon.