Brand will have difficulty suing her for libel because she's in the US. Is he going to face extradition if he's charged? It's a legal minefield.
Then there's the entire question or syndrome of people, ordinary people, interacting, having relationships with very famous people. This imbalance can cut both ways. Life, alas, is rarely as simple as Cinderella. The 'prince' often dumps poor Cinder and marries a real princess. What a shame.
People often remember sexual encounters very differently. One person's casual sex, is another person's first step towards true love. People 'misremember' the past and interpret events and actions, that happened years ago, with how they see the world now, not how they saw it previously, and have a tendency to create a new narrative about past actions based on what they feel about them today, which complecates things enormously.
Brand is up against, what amounts to a cult of highly movtivated feminist journalists who despise the patriarchy and alpha males like Brand and want to destroy and topple both. Brand becomes a symbol of everything they hate about male behavior and inequalities between men and women.