Fanny Robin is cheated by her lover Sergeant Frank Troy. They plan to get married, but when she turns up late to the ceremony, having gone to the wrong church, he uses this as an excuse to jilt her. This is all the more shameful on his part as we learn later that she is pregnant by him. Naturally, she is devastated, and ends up falling into destitution.
Troy runs into Fanny again when he is married to Bathsheba, and he does try to help her financially, but it is too late; she dies, unmarried, with her little child.
Troy’s abrupt abandonment of Fanny, for no good cause, shows him to be callous and entirely untrustworthy; yet when he meets her again he appears overcome with remorse and does what he can to help her. In fact, in a highly melodramatic chapter, titled ‘Fanny’s Revenge’, he declares his undying love for her over her coffin, to the absolute horror of his wife Bathsheba. In characteristic fashion, he refuses to take responsibility for his own actions:
If Satan had not tempted me with that face of yours, and those cursed coquetries, I should have married her (chapter 53)
Troy, then, does not really blame himself, but others – the devil and Bathsheba herself - for his own reprehensible behaviour towards Fanny.
It seems as though Troy just doesn’t like the idea of marriage, of being tied to any one woman; he also tires of Bathsheba quickly enough once he has married her.