Can anyone help me understand my tax code please.

[Yellowbowlbanana]

Sorry for the incredibly dull question but we've had a real wake up call when it comes to finances this year. We previously handed everything over to an accountant but it turns out he was a bit shit so I ended up with a huge, unexpected tax bill this year so I have been trying to figure it all out. I thought I'd got it sorted but have had my tax code for next year and can't understand how it has been worked out.
I have quite a complicated financial set up. I have two jobs, am a director of a LTd company which I receive dividends from. I (we) also own a BTL property (accidental landlord) which we draw a small income on (although we don't as it pays the mortgage but it is our pension).

The letter says:
This is how we worked out your tax code:
Personal allowance: 12570
Less higher rate tax adjustment: 146
Less Dividend tax: 7045
Total tax free amount £5379

Am I paying a Dividend tax of £7045 or are my dividends being used as part of my tax free allowance. If so, why is this the case?
Why doesn't my tax free allowance just get taken directly from my first salary? I don't understand.

Please help!

Dividends are taxable other than the first £2000
HMRC are assuming that you will receive dividends this tax year in line with what you received last year
They want to collect the tax during the year (
not wait for you to do a tax return and then send you a huge bill) and so they collect the tax on these through your tax code by reducing the tax free amount you can earn
If you end up receiving more dividends than they have estimated, you will owe more tax at the end of the year, and vice versa if you receive less then you will have a tax refund