as young age remember my being was full of compasion, for people, for animals, as soul become forgoten in schools and violent outerity world, suffered lost of deep compassion, what is wise way to get back that deep feeling ?
First, help others. Volunteer. Do something kind for someone else, without expecting anything in return, not even the feeling that you are giving. Labor on behalf of others. Even if you do not yet feel compassion in your heart, live compassion in your actions, and your heart will follow suit.
Second, you seemed to indicate that a type of suffering had hardened your heart. Transmute that suffering. Use the same suffering that previously had hardened you, to melt your heart again. Reflect on that suffering, and the pain you felt, and then reflect on the suffering of others who are close to you, and their pain. Come to realize that they have pain too. And just as your suffering has endowed you with a desire to no longer feel that pain, be able to see and feel that desire in others, and also come to wish that they will no longer feel pain. Start with those who are close to you, whom you love and hold dear, and gradually work outwards to include all living things.
Third, conserve and transmute your sexual energy. In the Tantrayana teachings, Bodhichitta (compassion) is equivalent to "semen." If you are losing the ens semenis (essence of the semen, sexual energy, in both males and females), that will corrupt your heart. There are many resources on this site regarding transmutation. If you need help finding practices related to this, let us know.
Fourth, related the above, be careful with desire. The more our mind and heart are corrupted by egotistical and selfish desires, the less we will be able to experience and express compassion for others. Work to eliminate selfish desires so that more of your being can be dedicated to helping others.
Finally, pray. Even if you cannot yet hear the answers, pray anyways. Express to your God that you wish to develop this compassion. Ask for assistance from your Inner Being, or a great Master whom you admire. If this is a sincere longing of your spirit, your Being will help guide you and help you.