Well, certainly so far as the marriage is concerned, you have grounds to divorce your husband on unreasonable behaviour. That's the easy part.
As regards the finances, if you are the higher earner you may end up better off than you are now if you separate, but that depends on too many factors for me to be able to advise in detail. You need to see a local family solicitor, see www.resolution.org.uk to find one nearby. I'd suggest that you meet with two solicitors for a free half hour's advice, and go with the one you feel most comfortable with in terms of professionalism and understanding the issues quickly.
The procedure is that you and your husband will need to voluntarily exchange Forms E (a detailed financial statement), whilst the divorce proceedings are trundling along. Once Forms E have been exchanged, both solicitors will have a clear understanding of the details of your case and will try to broker an agreement between you. It's only if those negotiations fail that you'll have to go to court for a judge to decide.
So far as the children are concerned, so long as the children are not at risk of harm during contact visits you should encourage and facilitate regular contact between them and their father. If you do have serious concerns then it may have to take place in the short term at a contact centre.
None of this comes cheap; it's unlikely that you'll qualify for public funding as you say you have a good job, so you need to pay your solicitor as you go along. You can keep your bill down in two ways; firstly, don't use your solicitor as a counsellor. If you want to talk about your feelings, do so with a friend over a bottle of wine. Your solicitor is being paid in six minute chunks of (usually) £20 plus, so an hour talking about your feelings is going to cost you upwards of £200. Secondly, do as much of the donkey work on the finances as you can; provide all of the documentation (bank statements, payslips, up to date evidence of the debts etc) in full, in date order, and in logical order. I have had to charge clients many hundreds of pounds more than necessary when they've dumped carrier bags full of random bills, receipts, bank statements on my desk which I've then had to sort out.
Hope you get on OK, remember this is going to be tough for the next six to twelve months, but you will come out at the other end in a better position than you are in today.