Help! My husband's bestfriend is trying to extort money from me after we had sex

Miss Petite I need your readers advice please. I'm 28 years old and been married for 2 years with no kid.My husband best friend who has been away for years came to Nigeria on the 3rd of this month for a project and I don't know why but he was so caring and always complimented me even when my husband failed to notice my new hair or look.He had this beautiful girlfriend who always came to see him

On my birthday which was the 12th ,my husband traveled to England for what he called an urgent business deal leaving his friend and I.I didn't plan on celebrating it but he forced me to go out to dinner.He said his girlfriend was going to be there.We went to the venue and he started telling me about their escapades in the University .I was cool with it till he said my husband had a girl he wanted to marry but he couldn't because she was Igbo .My hubby and I are yoruba. When I asked where she is now, he said she lives in London and has remained single since then.
I was heartbroken because I know my husband has been visiting the UK a lot and he never told me about her.He said I was his first love.I believed because we got married 8 months after we met .

I didn't know when I started crying and we went home.I don't know what happened but we slept together and it was after it was over I realized I made a big mistake and confronted him.
He laughed and said it was ok and told me it was a mistake and he would never ever tell anyone.
My husband came back 4 days ago  and I just couldn't confront him and ask about his first love since I know what I did with his friend.
I was starting to push my fling to the back of my mind last week my hubby's friend  asked to borrow some money from me. I told him I didn't have the money he was asking for which was 500k. He said it wasn't a loan, he said it's either I give him or he tells my husband what we did.He said I didn't deserve his fiend anyway and called me cheap.

I'm confused and can't tell any of my friends because I don't trust them. I also don't know if to confess to my husband first before he black mails me. Knowing my husband, it will be over and since I don't have a kid ,there is nothing tying him to me.Also I am not from a rich home though my husband spoils me alot
 Should u just pay his friend or tell my husband first? Please don't judge me

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