Concealing and Revealing Peoples Faults

Q: I did a certain sin. Now somehow my friend came to know about it. If he asks me whether I committed the sin, how should I reply to him:

1. Cover up the sin

2. Always speak the truth.

Q: I lied to my parents, my family, husband, his family and others that I did not love anyone before marriage. My husband found out but I denied it because I truly love my husband and my daughter. I did not want to lose them, is it a sin to lie like this? Will Allah forgive me? Will Allah help me?

Q: So, one of my cousins accuses me of talking negative about her behind her back at the time we were good, I'm not that close to my cousins who live locally near me although I want to be, so I was close with this one cousin she accused me of talking negative about her behind her back and she didn't give me time to explain and ignored me, I never once talked negative about her behind her back, before she ignored me she finished the chat saying she wants to cut me out of her life forever, months later my parents tried to get her and me to start talking again , she then told me that someone said that I had been backstabbing her, i was shocked since I never talk to anyone in my family (meaning cousins) and I wouldn't talk about her behind her back anyway , I then asked her what did I "supposedly say about you" as in what did this person say to you that I apparently had said , I also asked her who said this about me, she said No I can't tell you because I'm the Quran it says that breaking a promise whether it is bad or good is haram , I then said why would you tell me that someone said that I said something negative about you behind my back yet you won't tell me what they said or who they are ? Is it a bigger sin to cover up for another persons sin and not tell the victim what has been said? How am I meant to get self justice for myself. Till now my cousins still ignore and now have been arguing with my brother "exposing sins"

Q: I would like to ask if someone knows the truth and is hiding it from others in order to save the bad person or guilty one, what does the Qur'an and Hadith say about it?

Q: Can a Muslim reveal the faults of a non-Muslim?

Q: I know we shouldn't advertise our sins. I mean we shouldn't tell others about our sins. I was told if you tell others about your sins, your sins wouldn't be forgiven. Can I able to tell an imam or a scholar so they can advise what to do about my sins?

Q: If a young girl is sexually abused and when she grows up, does she have to tell her husband when she gets married because marriages involves honesty. If she does not tell, she is keeping things from him. Is that allowed?