And the heart must pause to breathe, (7)
Pausing to take a breath? We're guessing this isn't because the speaker has just finished working out. He's pausing to breathe, but we think he means pausing and sighing and reevaluating his life. That's what dissatisfaction does.
And love itself have rest. (8)
This is just like line 7. It's not that the speaker is so tired from all his loving. No, no, no. It's "rest" in the sense of a break, a cessation for good, because love is no longer a source of satisfaction. That's sad.