You want to hear it? well:
Only, my secret's mine, and I won't tell.
Or, after all, perhaps there's none:
Suppose there is no secret after all,
But only just my fun.
Today's a nipping day, a biting day;
In which one wants a shawl,
A veil, a cloak, and other wraps:
I cannot ope to everyone who taps,
And let the draughts come whistling thro' my hall;
Come bounding and surrounding me,
Come buffeting, astounding me,
Nipping and clipping thro' my wraps and all.
I wear my mask for warmth: who ever shows
His nose to Russian snows
To be pecked at by every wind that blows?
This line has several interpretation, but continues the  extended metaphor . This plays back to all the previous lines about letting the draught in. She had two forms to represent protection: the house and the warm clothing. Nipping and clipping are penetrating and invasive by small stages. The suitor might have emotionally entered into the heart. 
 Sidenote:  If this refers to a woman, specifically Rossetti, it could be seen as sexual penetration.
Winter: My Secret