I don't really get what happened to blase, Amy, and Jeremy. Was it like a love triangle?
Kind of.
It’s a bit complicated, so the explanation’s under the page break:
Blaise and Jeremy started out as just friends with benefits, with Jeremy more “into” the relationship aspect than Blaise. They were getting along pretty well for a very long time, kind of dating, but also not (if that makes sense). Their relationship wasn’t traditional, but it was obvious that they deeply cared for each other.
But then Jeremy got stabbed in the chest with a knife and almost died. When he was in the hospital, Blaise was FREAKING THE HECK OUT. She couldn’t handle the thought of losing him, so she stayed away. I think she only visited him when he was unconscious, but being so close to his near-lifeless body REALLY hit her hard. She was super scared of him affecting her like that, so she tried to distance herself from him so that she wouldn’t feel the pain.
Jeremy wakes up and gets out of the hospital. To his knowledge, Blaise wasn’t there for him. She was the last one to “visit” him. She should have been by his side when he needed her most, but she wasn’t. He has no clue of the freakout. Blaise ends up breaking off their relationship with little-to-no explanation why. Jeremy’s super hurt and angry by this.
Amy then turned into a “rebound girl” of sorts. She was everything that Blaise was not. Sweet, caring, and there for Jeremy. Like two days after breaking up with Blaise, Jeremy gets together with Amy. They both really like each other, but Amy’s hesitant about the new relationship (as she should be). She says that she won’t continue seeing him until he tells Blaise that they’re together. Jeremy takes his damn time doing this. Really, it takes forever.
During this time of Jeremy being angry at Blaise (and him dating Amy), Blaise is in a horribly unstable state. Her past has come to haunt her, and her guilt over killing Kolo (the dude who killed Ken) is hurting her. She goes to therapy and tries to fix her mental state, but it’s super hard. It doesn’t help that Jeremy’s a jerk to her every time they meet. Slowly, she starts to fix herself and finally realizes that her fear of losing Jeremy was because she loved him. But it’s too late now, Jeremy’s moved on.