Do you have video of him having s*x with that woman? If yes, you can get divorce for sure, if not it is impossible to get divorce from your husband.
However, point here is why dont you give rejuvinating the marriage? Try pump in some fresh blood into the marriage, why does your man seek pleasure outside? Simple reason is you have failed to provide it at home.
Anyways, think about reconciling, divorce is not easy, its after effects are not either. Better think than be sorry.