It feels kind of awkward making this comparison on something that was drawn when the original series hadn't even finished its run yet. But...
I look at this and it instantly reminds me of what happened with Homura after she cursed herself. The flower field scene, that is. I wonder if this is what Sayaka saw just after she went over the brink.
She takes Hitomi up on her offer and confesses. She gets rejected. The other girls come to try to cheer her up (or, in Homura's case, either comment on how she knew this would happen or just shadow Madoka). It's appreciated, but it doesn't work.
Then Hitomi comes and one of the following happens:
She got rejected too.
She tells Sayaka her real feelings are for her.
She didn't confess because her friendship with Sayaka means more to her than her potential one with Kyousuke.
Bottom line, she wants to save their relationship, and Sayaka does too.
But she knows this is an escape fantasy. It didn't happen, it can't ever happen, and that last thread of her hopes and dreams dies and all she can do is drown in despair, literally and metaphorically.