In John Donne's "The Flea," the speaker is not expressing his love for the woman to which he speaks, but his lust: for his argument about the flea is his attempt to convince her to sleep with him, a plea that she has been resisting.
The speaker argues that as the flea has bitten both of them, their blood is mingled and they are more closely tied, as they would be should they go to bed.
It sucked me first, and now sucks thee,
And in this flea our two bloods mingled be...
He goes on to assert that in joining their blood, nothing shameful has taken place: she has not slept with him, lost her virginity, or done anything that would upset her parents. But he notes that the flea did as it pleased with her, without having to win her, as the speaker is trying to do. He explains, then, that they are joined in the blood of the flea, and this is something of a "marriage bed." And he reminds her not to kill the flea, or she will be killing not only the flea, but also herself and the speaker...at least in terms of this unusual union.
He asks her:
Cruel and sudden, hast thou since
Purpled thy nail, in blood of innocence?
Has she squashed the flea?, he wonders. For if she has, she will have murdered an innocent victim, for the flea was not a guilty creature. One may assume that the argument falls flat on its face, in that it does not convince the lady to acquiesce.
Her quick response with her nail in the face of this man’s elaborate plea suggests her response to his final assertion as well.
There is no mention of the speaker's love, abiding or gentle: he simply argues why they should have sex. This is not a poem of love, but of seduction by logic as the speaker tries to give irrefutable evidence to convince her to stop her resistance to his advances and give in.
(This is a poem of Donne's earlier years, when he was known "as a frequenter of ladies," before he married, changed his behavior, and became "the dean of St. Paul's Church." This further proves Donne's less than noble pursuit of the woman in the poem.)