Am I taking this too far ? My best friend refused to share her own husband with me ?

I love my best friend like a sister cause we are both the only child of our parents and we grew to love each other so much .
Went to same school till our university level and did our NYSC together . Their was no me without her to the extent that we made love and shared our men , yes we were that close . Life was so beautiful with us until she found love and decided to get married , for the first time my best friend refused me sharing her man with her so I respected her opinion . They got married and am stil dating but got engaged few months back.

I got engaged to one of my ex who we came back together and things worked between us , my wedding is next month but I just found out that my best friend has been cheating on her husband with my boyfriend . I caught them red handed in the car ba.nging each other without a c.ondom, I was mad but refused to act stupid , when my best friend came to apologize I understood with her because we have both shared him in the past , but why my husband to be ? why she refused to share her own husband . So I gave her 2 conditions , either she allows me sleep with her man or I tell him that she cheated .

She has refused so I think I will tell her husband,As for my wedding I will not call it off , I will still marry him but I must cheat in return .

Last night my mum told me that am a wicked friend and am going too far , that is why am sending this story to get public view on this matter .

Am I taking this too far ?