Found: Funny British novel about man with secret apartment in London with fish on cover

Hello, I read a comedic novel about 10 years ago about man who had a family but had a secret apartment with some flat mates across the river to get time away from his wife. He didn't really enjoy the little everyday things like taking care of the kids, he would rather be a bachelor.

One day, he goes skinny dipping with a girl and he almost cheats on his wife. He ends up confessing everything to her and she forgives him. He learns to enjoy the little things in life, realizing that that is truly what life is about.

Anecdotes I remember:

Him and his wife getting pulled over and pretending to not speak English.

His flat mate would always be confused when books and movies said, "And one thing led to another." He was like, "But HOW does one thing lead to another?"

Notes:

- Set in London
- Comedic
- And I swear I remember a fish on the cover

Thanks for your help!!

>1 BookishHorseGurl: Hi, I believe you are looking for The Best a Man Can Get by John O‘Farrell

>2 vroni: Beat me to it.

Yes! That's the one! Thank you so much. It was during a sentimental time, and I don't want to forget it.