1 Corinthians 7:4:
A wife is not the master of her own body, but her husband is; in the same way a husband is not the master of his own body, but his wife is.
It is not the wife who has the rights to her own body, but the husband. In the same way, it is not the husband who has the rights to his own body, but the wife.
That’s the gospel practically played out in marriage, mirroring how our bodies belong to Christ because he purchased us at the Cross.
I don’t think there are too many intimate acts that better demonstrate the principle of a man’s body belonging to his wife, and hers to him than him drinking her breast milk daily.