Hector is pretty much defined by one act: stealing Helen away from his best friend, Achille. It's not a very honorable way to behave—and certainly not what his ancient Greek forbearer would have done. Once best friends on the sea, Achille and Hector become instant enemies over Helen, and we see them on the shore, slashing away at each other with cutlasses (just like the ancient heroes of the same names). It's a bro-tastic bummer.
It isn't terribly clear why Hector's motivated to purchase the Comet and leave behind his beloved life on the sea—we're told only that the transport van was where "he had stepped between Helen's/fight with Achille. Why he had bought [the] chariot/and left the sea" (XXII.ii.118). Does this mean that Hector steps away from the bad situation with his friend and leaves Helen behind as well (but she follows him)? Or is Hector merely avoiding Achille because he now has his lady? We'll leave that up to you to decide.
We do know that Hector misses the sea, but we don't get the full reveal of his state of mind until we see him slumped over the dashboard after his fatal accident: "He bowed in endless remorse,/for [the Virgin's] mercy at what he had done to Achille,/his brother" (XLV.i.226). In other words, he holds love in his heart for his BFF until his last breath, making it clear that it isn't just the salty water he longs for.
Unfortunately for Hector, the grass really wasn't greener on the other side of the island for him. Though he'd hoped to modernize himself and perhaps get ahead financially, his career change (from sea to taxi) instead highlights for him the huge mistake he makes in leaving the sea behind—he just loves it so much.
The bummers just keep coming, though, since it turns out that buying the transport van isn't his only mistake of the heart. His desire for Helen is also a misinterpretation of his own emotions, as he only "longed for [her] from a distance" (LXV.iii.231). Once he actually gets her, though, he's not so enamored.
Hector loses more than his best friend in the process—perhaps even more than his life. Because he forsakes his true love (the sea), Hector becomes a haunted man, rash in his daily actions. It turns out that his time on the ocean gave him time to be at peace and develop his spirituality, something he hadn't considered in his estimation of life spent in the village:
[…] In his lost canoe
he had said his prayers. But now he was in another
kind of life that was changing him with his brand-new
stereo, its endless garages, where he could not
whip off his shirt, hearing the conch's summoning note. (XLV.iii.231)
Walcott parlays the remorse that Hector feels in his dying moments into a cameo appearance of the road-warrior in hell. There, the narrator-poet encounters him decked out in full regalia, like a Trojan hero ready for his last, desperate battle. Walcott tells us that he's there not so much because of his disrespect for Achille—it's because he chose the wrong side. Again:
[…] not for Omeros's gods
nor the masks of his origins, the god-river,
the god-snake, but for the One that gathered his race
in the shoal of a net, a confirmed believer
in his own hell, that his spectre's punishment was
a halt in its passage towards a smokeless place. (LVIII.ii.292)
Hector can't be redeemed (like Ma Kilman is, or Philoctete) by a return to his original life and to the ways of his ancestors. Like the warrior whose story Achille hears during his stay in the settlement of his ancestors (check out XXVI.i.139), Hector "disinherits himself" by forgetting his people for "an albino god." Remorse comes, but too late.
Hector has to follow through with his decision to partake in the ways of the encroaching world into his afterlife. In this case, he's dealing with the fallout of his acceptance of Christianity. But Walcott gives both Hector and us a bit of hope: At some point, his soul will move on to a "smokeless place," where the narrator-poet expects to catch up with him. It's more like a time-out than eternal damnation for Hector, then. Phew.