cheaply, the speaker is admitting that he received very little in return. The experience in loving someone else just was not worth the price he paid. At the end of this quatrain, the speaker reveals that he has repeated these actions of loving others on numerous occasions. The expression "old offenses" suggests that he has been behaving like he did when he was younger. As a young man he had loved many people without thinking about it -- without being rational. But now, even though he is an older man, he has been repeating that same foolish behavior with "new affections" or new loves.
The speaker continues to admit his mistakes in the second quatrain, but adds that something worthwhile has come from his experiences. The quatrain begins with the speaker stating that by loving other people, he was avoiding the "truth" (line 5). He knew deep within himself that he should not have been with these others. But he had avoided this truth: he allowed his passions to cloud his judgment. But (and the speaker uses the word but in the middle of line 6) the speaker adds that these experiences, these mistakes ("blenches"), made him realize, deep within his heart, that his true and only love was for the young man. He states that the experiences "gave my love another youth" (line 7). He means that his heart became revitalized. He finally realized the truth. The speaker hopes that the young man believes him. And the speaker even swears "by all above," suggesting both God and Heaven, that what he is saying is the truth. The quatrain ends with the