it's better to wait, but depends how far his divorce case has gone..
from a OISC immigration lawyer
The fiancee visa application will be accepted if you can show that the divorce will be finalised within the six months of your visa, so that you can get married. So, if you have the decree nisi, you should be okay. Otherwise, a letter from your divorce solicitor confirming this usually works.
However, if the divorce is not likely to be finalised within the six months then the application will be refused, so it would be best to wait. If the petition has not yet been served then it is unlikely that it will all be sorted so quickly.
