You wish it were head cannon. Point to one time Zoro had a response to a woman. He responds to swords and booze, but not to women. Oh, wait, he responds to the Sword EMMA, and Emma can get him going.
However, since Emma is a sword, Zorro is asexual. This shouldn't upset you because Zoro being asexual lets him entirely focus on his dream of becoming the WSS, without distractions.