FIRST TIME BUYER CREDIT SCORE?

I am trying to buy a property i have a score of 779 a deposit for the property i want.
i am self employed with 4 years off returns
i recently got refused credit (mortgage in principle) a few months ago and turns out it was because of a financial association with a ex partner. I have removed this association with expierian credit i am just wondering if /…
A) 779 is a high enough score
B) if i will have to remove this financial connection with other credit expert companies

the association was a joint account

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