This is a passenger list for Walter's arrival in London 26 Jul 1908 giving his wife's name as Mrs Ida M Allport:
https://www.ancestry.co.uk/interacti...=successSource
Here is another family tree on Ancestry which also gives his date of death as 6 Apr 1930 and which says he was buried at the Gout Cemetery in Dominica. It shows him having quite a few partners but most of their names are hidden so I don't know whether Marthe / Marta is included:
https://www.ancestry.co.uk/family-tr...01080144/facts