Russell Brand is reportedly concerned he "gave up" on his marriage too quickly.

The British star is in the process of getting divorced from Katy Perry, after they confirmed their separation in December.

Russell has been spotted with several women since then and Katy is also thought to have moved on. She is currently rumoured to be dating Florence + The Machine guitarist Rob Ackroyd, with the pair spotted canoodling at a recent music festival.

The images are said to have got Russell thinking about the way his life is heading.

"Word has it Russell was seething with jealousy' when he saw pictures of her with Rob. He apparently feels he gave up on their relationship too easily," a source told the British edition of Grazia magazine.

Russell is believed to have penned an email to Katy is which he talks about the demise of their relationship.

The 36-year-old supposedly admitted he had been hasty when it came to their split and now sees it as one of the worst mistakes he's made in his life.

Although 27-year-old Katy is thought to have appreciated the gesture, she is happy with her new life.

"It's fair to say that Russell only wishes Katy happiness," the insider said. "But perhaps he should have realised just how special his wife was when he was married to her rather than five months later."