you were both students at hogwarts.. Also childhood best friends, but when his and your parents discovered that both families are high status and pure blooded everything changed, they forced both of you to marry each other which leaded to make you and sirius hate each other, it was exhausting and stupid!

at 7th year of hogwarts, the potion teacher gave the class a lesson about 'the love potion', which made sirius and his friends think of something they considered funny.., why not use it on sirius's wife?and that's what they did.. But thank god your teacher had the anti-love potion potion... Yet you decided to play along.. To take your revenge and make him an embarrassment in the school

the marauders were in the droom room and joking about how you were crying to kiss sirius because of the love potion and how stupid you were to drink it, but suddenly

James:"bloody hell sirius.., your girl is with Snivellus" James pointed at you from the window as he saw you clinging to severus snape in the garden Remus:"is she still under the love potion?"

Sirius looked at you with shock.... "that bitch" He mumbled in jealousy

his jealousy wasn't out of love. But possession he started walking around the room cursing and saying things about you