Complex sentence: Tom comes home from the West later, and even though in his letter he said he loves Maria Bailey, he only said so because Polly's brother did not want anyone to know that he (Polly's brother) loved Maria.
Split into simpler sentences: Tom comes home from the West later, even though in his letter he said he loves Maria Bailey. He only said so because Polly's brother did not want anyone to know that he (Polly's brother) loved Maria.