Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
What is your financial position?
How long have you known each other?
I am afraid the Uk does indeed recognise his marriage not withstanding the lengthy separation
However this does not preclude him coming here on a Fiancee visa on the basis that after 12 months residence her he will be able to issue a divorce petition based on that separation
the details of eligibility - and how to apply - are here
Please ask if you need further details
That is a marriage visa.
The actual term for the visa you would apply for is a "family of a settled person visa" - you would need to engaged to fulfil the requirements