Flynn might have stuck on Emma for sometime so Ivy wouldn't get through to her, but he can't protect her from the truth always. Ivy patiently sought out opportunity to speak to her, never the less she was on guard, risking her long-time relationship with Flynn who was there for her in her emotional stress for a person she barely knows was indeed a risky act.
During this Lisa went through her heart breaking break up, she never stopped in trying to clear things with Levi, Levi who was totally uninterested in what she had to say he ignored her text messages, her calls and even her advance all this cause of Ivy.
It is painful to watch Lisa go through a lot. The way the entire school was it was damn love triangle, Lisa finally loves Levi but now he has gone back to his middle school crush Ivy, Ivy on the other hand was plotting another person's break up, Emma and Flynn were the only recognized legit relationship still happening with so many strings attached.