[…] It's hardFor fathers to compete with mothers' love. (7-8)
The speaker in this poem admits his own competitiveness with his wife. It's as if he's taken a moment outside of the action of the poem to acknowledge, yes, even parents sometimes compete with their spouse for the title of "Most Loving Parent of the Year" award. But this is only part of his reaction to the action of the poem. We get taken through the speaker's experience as if we have backstage passes to his psyche, and not only does he get jealous of his wife, but also his son, and later, starts to turn in on himself to find out what's up with feeling so competitive.
Dull and jealous, I was the smallest partOf the whole. […] (10-11)
Here, we have the speaker admitting that he feels, um, small. Like, itty bitty. As if he is the most insignificant part of the family. So small in fact, he thinks he'll go unnoticed by his own wife and son.
But I felt less important than the farthest star
As my wife fed my son in the hungry dark. (12-13)
These two lines are divided by a stanza break. The speaker does a good job juxtaposing the word "star" with "dark." Just like there's some conflict between the rhyming words of the poem, there's a bit of conflict between the speaker and the people he loves. He's bound to his wife and son because he loves them, but paradoxically feels completely isolated from them. How weird is that?