David Feintuch: Fisherman’s Hope [1997] paperback

Commandant Nicolas Seafort is a legend to the masses, an idol to his hundreds of teen cadets. They don’t see the tormented soul of a man who believes that merciless duty has led him to betray every friend he ever loved, every ideal he ever cherished. After a life-long ordeal, Seafort needs tme. Time to reflect. Time to heal. Instead he is pulled into a maelstrom of crisis, corruption and danger as the helpless, unprepared Earth faces annhilation from a hord of alien attackers. Alone at the centre of a cosmic apocalypse, Nick Seafort must face his final battle…and his most unforgiveable sin.