i think the first part is about regret for being a coward or for causing someone they love trouble because of this person's own personal failings.
the second part i read as this person saying they feel so much emotion that their heart is "bursting" and that whoever they have wronged is so important to them that they will "leave a mark" and they can already feel this person's disprovable or disappointment.
the third part i think is is about they're failings as a person again. this part seems very self-deprecating and seems to be about them recognizing all these terrible things that they are and basically coming to terms with it because they cant help who they are.
i think the first part is about regret for being a coward or for causing someone they love trouble because of this person's own personal failings. the second part i read as this person saying they feel so much emotion that their heart is "bursting" and that whoever they have wronged is so important to them that they will "leave a mark" and they can already feel this person's disprovable or disappointment. the third part i think is is about they're failings as a person again. this part seems very self-deprecating and seems to be about them recognizing all these terrible things that they are and basically coming to terms with it because they cant help who they are.