Weird dark comedy film about an estranged family

So I saw this movie a few months ago on Film 4 in the UK. I think it was British though it may have been american. All I remember is this couple who live by a lake in a big forest have a dog and one day the husband is out walking the dog and meets this man who comes back to the house for a drink. The man ends up staying the night. The wife is not happy with her husband for allowing this guy to stay and they have a big argument the following day. The husband tries to make up by getting some of the wife’s poetry and showing it to the man he invited round. The wife ends up destroying it. At some point in the film, out appears the man the husband met in the woods appears to have some sort of mental breakdown and kills the couple’s dog while walking it. At first he pretends he found the dog dead as he appears to not understand what possessed him to kill this dog. Later on, the couple’s grown up children come to attend the funeral for the dog.

Does anyone know this film? I’m pretty sure the title has the word ‘lake’ on it somewhere. Thank you!

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