I know the definition of backbiting but I fail to apply it in some situations. I cant decide whether they account for backbiting or not..Please can u explain these situations individually
My relative always says negative remarks to me. I told it to my parents so that they keep small distance not to cut the relation.Is it backbitting? 
My classmate hurt me by telling that you look like dead body and always makes fun of me. I got hurt .I told my bestfriend just to feel better. Is it backbitting?
My friend told me that her friend was telling that i have no dressing sense. I replied to my friend that your friend has no right to tell this she wears so cheap clothes, first of all she should look at herself
Telling the behaviours of my cousins to my mother when i visit them. Is it backbiting ?
If i tell my sister about a girl who laughs at me, who once tore my book, who is very arrogant. Is it backbitting?

For start, read daily dua in mafthe ul jinah, and daily ziarat. All week days having different dua and ziarat. In all above 4 situation if your intention is good then it's ok.

2nd be positive to all makes you feel good and change your behavior and appearance also because zahair and batin both have to be good