If you go onto the USCIS.Gov website there is a form to petition for a fiance, I believe it is K129 or I129. I know you have to get married within 90 days of sending in the application. After that you can apply for a work permit in the US and a green card. However, should you divorce within a certain time period the person will have to return to the UK. Hope this was somewhat helpful. I am going through the same thing right now but we are getting married in the UK and filing there so my boyfriend can keep his job whilst we receive the entry visa.