Mordiar's Hymn. Mordiar's Opus, #3

Mordiar Morduk was at pinnacle of his career. One of the youngest space-marines to achieve the rank of Maxim Quirinus, he had won every medal the Confederation offered, a few of them more than once. Then one day he was branded as a war criminal and forced into exile or be executed. For twenty years he has been hiding out on a planet trying to get through its industrial age, finding peace and solitude, his only real companion a combat-mech named Bob.
Then he meets Cheyenne, a sixteen year old just off the stage-coach and over the next two years he finds that for the first time in his life, he has fallen in love and is ready to start a family. The leaders for the Rebellion show up then and ask him to join in their life-or-death struggle against the Nergal Demesne, who defeated the Confederation in a civil war and now threaten to bring the entire multi-verse under their dominion.
When he refuses, Mordiar has no idea that he has set a chain of events in place that will shatter his life and throw him into the middle of and even larger and bloodier conflict as the Nergal Demesne will stop at nothing to bring him to justice. Thus starts the Mordiar Opus Trilogy.