I wanted to know if:
1)One falls in sin of backbiting or listening bad of others, should he apologize with that person about it or asking forgiveness from Allah swt is enough? And he has have to apologize from the particular person?What is he supposed to do if he fears that their relationship or brotherhood spoils ?
2)What are we supposed to do if we didn’t want to listen bad about others and that falls into our ears unwillingly?

Gheebah or talking bad about a person or people in their absence is mentioned in the Holy Quran as an evildoing and like eating the flesh of ones dead brother which is deplorable.
However, the doors of forgiveness are always open to a believer who does not wish to repeat his mistake and truly asks repentance to Allah s.w.t.
It would be a good thing to ask the person who was talked about for forgiveness, although in most cases, the ill feeling would tend to increase. Therefore, one can take out sadaqa for the person and try his best to spread good words about him wherever he talked evil about the person in a manner that he should be honored in front of those who regarded him a bad person after hearing the gheebah.
It is best to retain good relationship with the person so now one should try their best not to speak anything behind him and amend their relationship of brotherhood.
A true believer will always try his best to stop listening to gheebah as well. In a gathering for instance, one can either excuse one self, or say good about the person when hearing things spoken against him, or even try advising the people around him of the severity of punishment for whose who do gheebah.
All in all, continues repentance should be asked by the one who engages in such an action.