Hear, o gods, my desperate plea To see my love beside me Sunk below the mortal sea Her anchor weighs upon me
Orpheus is trying to say that with Eurydice death and leaving him, he feels something pulling him back from happiness, so he prayed to the gods, saying to bring his love back so he can be happy.
Everywhere men sat shackled in sorrow, expecting the worst, wishing often he and his kingdom would be conquered.
No one liked Earmonric that they wished they were conquered. This shows that Earmonric is not a very good king. The thought of their people getting conquered is better than being ruled by him, he must have done some terrible things.
Favors will be returned, debts will be repaid. Do not forget your manners.
The author is trying to say that because of helping other people with things they need, they will help you back. Helping others make them like you, so they will help you back.