Other BondsThere are three other characters in the series that leave a mark on Sayaka in addition to Kyousuke and Kyouko. Ironically, though perhaps to be expected as important people in her life, Madoka, Hitomi and Mami all ultimately end up contributing to both her despair and growth in some fashion. Each character says or does something that contributes to Sayaka's breakdown, but does something else that helps her grow as well.
Kaname MadokaMadoka is Sayaka's best friend. They are clearly very close and would do anything to protect each other. Madoka is always very supportive of Sayaka and wants to do anything she can to make her happy. She worries about Sayaka's depression and tries her best to stand by her friend's side as a non-magical girl. Unfortunately, the more Madoka tries to be helpful, supportive and a good friend, the more Sayaka pushes away. As Sayaka's self-hatred increases, she has a harder time believing that Madoka could really care about her. Sayaka feels she doesn't deserve her concern because she is a bad person and isn't even human anymore, anyway. Further, Madoka could become a magical girl to help her and won't. Therefore, despite Madoka's good intentions, she ultimately ends up pushing Sayaka over the edge by making her feel even more alone. Sayaka gets word from Kyuubey that Madoka has the most potential out of all of them. Madoka, unlike herself, could easily defeat witches without breaking a sweat. And yet, she refuses to make a contract. Despairing, Sayaka displaces her frustration on Madoka. If she really wanted to help her, she would become a magical girl, too. I personally think that even though Madoka always stood by Sayaka's side, not wanting to be a magical girl was perceived by Sayaka as rejection. The only part of Sayaka's identity that she felt she had left was being a magical girl that fought witches. If Madoka rejected the idea of being a magical girl, she was basically rejecting Sayaka's identity, too. Of course, Sayaka realizes she is being ridiculous and putting her own feelings on Madoka, which makes her feel even worse for hurting her best friend. Her last interaction with Madoka seems to be the straw that broke the camel's back, as it was the last personal thing that occurred before she turns into a witch. However, Madoka does end up saving Sayaka, too. She literally saves her by having her become part of the Law of Cycles before she could turn into a witch. Also, Madoka lets Sayaka see Kyousuke play violin one more time before they move on. Sayaka remembers why she became a magical girl to begin with—something she loses in her despair. Madoka reassures her that her wish and everything she did for it was precious. Thanks to Madoka, then, Sayaka is able to take a step back from what happened to her and finally accept it with no regrets.
Shizuki HitomiAs Sayaka's second best friend, Hitomi is someone she holds dear. Hitomi's lasting impact on Sayaka isn't because they are best friends, however. Hitomi puts Sayaka in a very tough spot by confronting her about Kyousuke. Feeling cornered and scared that Hitomi will take Kyousuke away from her, Sayaka experiences a range of new emotions such as jealousy, anger, fear and guilt. Therefore, I think Hitomi's role in Sayaka's story is to challenge her previous level of emotional maturity and thus help her grow. Her confrontation forces Sayaka to grapple with how to deal with ugly emotions such as being so mad at your best friend that for a split second, you wish you never saved her. Hitomi also causes Sayaka's feelings with regard to her loss of humanity to rekindle and forces her to struggle with what being a magical girl means in terms of relationships. She's a catalyst for Sayaka's emotional maturity by igniting new and difficult emotions that ultimately end in her despair and eventual growth after being saved by Madoka. I would even argue that Sayaka's feelings toward Hitomi represent the stages of her gradual growth throughout the series. She goes from viewing Hitomi as a best friend, to not being able to stand the sight of her with Kyousuke and feeling like she's stealing him away from her, to acknowledging Hitomi is a great girl and that Kyousuke doesn't even deserve her. Therefore, although Hitomi's actions set off a chain reaction that results in Sayaka's emotional breakdown, Sayaka is able to mature and grow because of the experience.