Dafuq. What happened to Sensei having feelings for Suzu?
A couple of possibilities. One, she doesn't like grown girls. Two, she doesn't like experienced girls ("she's using sex appeal" plus the earlier reference to it requiring experience) and only goes for innocents. Three, not very likely, she doesn't like full-on relationships and gets tired of people quickly.
Most likely the second one. Sensei's a bit awful, really.