The one risk that changed it all.
Cheating with Daniel was the choice that changed everything for Issa in later seasons. By watching the show you can tell that Issa's character regrets her decision and still loves Lawrence but a small part of her was eager to be single. Issa begins making more clearly defined decisions in her life after cheating on Lawrence. She first decides that she would like to enjoy being single and not jump into any kind of emotional relationship. In fact she decides to make a "rotation" of guys simply for hookups. Issa becomes more blunt and upfront about what she wants from men. In a sequence of scenes where she goes on first dates with guys from different dating sites, Issa shows absolutely no interest in any of the guys sitting across from her. Remember the raps she used to do in season 1? well the raps have now become thoughts that are flowing through her mind but instead of rapping or just thinking about them, she's begun saying them out loud. Her personality has become more open, sarcastic, and straight-forward. Her sense of style has also taken a turn. Issa's character is clearly more confident with herself and her body in seasons 2 and 3 when she wears more brightly colored/printed shirts, skirts and dresses. However, her confidence in her newfound self waivers one day in her apartment when she realizes how much she still loves Lawrence. She looks at a stain in the wall (caused by a fire when she was hosting a party trying to get over Lawrence) and realizes that she messed everything up. The stain becomes this looming thing that stares at her whenever she walks into the apartment and it essentially represents her relationship with Lawrence: a blank, bleak canvas with a huge black stain at the top of it. At one point she looks around her apartment (which she used to share with Lawrence) and is overcome with emotion. She begins breaking everything around her and throwing things across the room. I think this breakdown symbolized how Issa felt in that moment: alone and angry. She was angry at herself for cheating but also angry that Lawrence had led her to it (even if he didn't know it). After this point Issa begins reevaluating everything. She realizes that the first step to moving on is to leave behind the apartment that shared all their memories together. Issa does this without having money or a plan of where to move to next, but she does it regardless because she knows it has to be done. The apartment represented many things in Issa's past and her decision to move out meant that she was attempting a fresh start. While moving out, Lawrence comes to pick up his things at the apartment and has a heart to heart with Issa. Issa confesses how much she still loves him, and he tells her that she wasn't the only one to blame for how things went downhill in their relationship. When Lawrence is leaving, the scene flashes to Issa's thoughts where Lawrence decides to propose right there in the apartment and they continue their lives together in the home that they essentially built together. Issa flashes back to reality but decides to let Lawrence go (who is now in a relationship). This shows a change of maturity in Issa and a willingness to let Lawrence be happy with someone else, even though she's still in love with him.