Tomorrow is for ever - E. V. Thompson

Alan Carter was only married to Dora for a week before being called up to serve in The Great War on HMS Viper.
Eighteen months later, convalescing from a shoulder wound, he discovers his wife has almost forgotten him - and fallen in love with an American soldier.

Devastated, he leaves East London for Cornwall. When his shoulder is better, even if his heart is still broken, he goes back into service and puts everything into it - getting two medals for bravery in the process. After the war he decides he might as well live in Cornwall - it is quiet which would suit his hopefully successful new writing career - and he can try and start a new life.
When he meets artist and suffragette Vicky, all looks much better...