It's really annoying how the author makes his main characters so unlikable by not letting them be able to say a few simple words.
"Sorry, I'm in a relationship." "Sorry, I like someone else." "Please leave me alone, I'm not interested in you." "Let go of me right now." "Leave me alone" "Who I love is none of your business" etc.
Sensei's coworker is a total cuntbag as well. But he's a cuntbag for letting her suck his dick. Is he really so unmanly and weak that he couldn't let her to let go of his arm, and couldn't get her to stop following him home? And based on what she's saying, she clearly already knows he's in a relationship, so why not just spell it out for her?