Why agree to an interest that huge in the first place? I put it to you that you didn't intend to start a business but put it into all these quick yield 'investments'. No true business person will accept that kind of interest.
For a 3 years relationship, you could not open up to your ex about your failed venture but instead continued lying. Hian! And the lies are still piling up as you are lying to your parents as well and now owe your dad N800k.
Tell your boyfriend you were duped and you will come up with his balance, borrow from your father if you have to again. I have an issue with the way your boyfriend has reacted though...good your characters came out.