They reanimate their hate of Luca to lower their remorse, but at every instant his blood stains their speech.

At last, while Ottima loves on, Sebald's dark horror turns to hatred of her he loved, till she lures him back into desire of her again.

The momentary lust cannot last, but Browning shoots it into prominence that the outburst of horror and repentance may be the greater.
I kiss you now, dear Ottima, now and now! This way?
Will you forgive me--be once more My great queen?
At that moment Pippa passes by, singing: The year's at the spring And day's at the morn; Morning's at seven; The hill-side's dew-pearled; The lark's on the wing; The snail's on the thorn; God's in his heaven-- All's right with the world! Something in it smites Sebald's heart like a hammer of God.

He repents, but in the cowardice of repentance curses her.

That baseness I do not think Browning should have introduced, no, nor certain carnal phrases which, previously right, now jar with the spiritual passion of repentance.