foe,

http://www.merriam-webster.com/dictionary/foe

The use of the word "foe" makes the poem clearer. To know that it means enemy tells me that the man who was murdered. Was murdered not out of despair or jealousy but pure hate. It points to the fact that this wasn't an accident. It was something that the speaker wanted but he now regrets. He says i shot him dead because he was my foe. However, no matter the form of murder or killing, people always always regret it, esspicaly those who have good souls.