they knew that when farm boy got so much attention from the princess. And how the princess said I am going to marry you on day and really loved him and not the rich snob of a prince wanted her to be his wife and not the peasant or the farm boys wife.
Infinitive is to keep. use is adverb. hope it helps.
remorseful is your best answer
"remorseful" means "filled with remorse, sorry". Even though it is not said, it is implied that he is sorry, because he thinks back to the history of how his mom ended up like that.
hope this helps