why jesse acting this way?

Okay, you have to realize that Jessi is not like Kyle. She had a really rough start..and she's still so new to life. She understands what things are, and people to an extent, which is more than what Kyle had when he started...but it was all downloaded, it's knowledge which is just there in her head, so she doesn't really...get situations. Plus, she's alot less cautious than Kyle is, like people on the show have said before, "She doesn't know when to stop." She sees a way to get a reaction out of people, and then she does it. She wants to help people, but doesn't realize how she does it could hurt others. She wants attention, and since Kyle has a life of his own...she often feels left out, and jealous of everyone who gets to spend more time with him. Which makes her act out, because she feels more entitled to be apart of his life than other people. And she feels hurt, and jumps to conclusions, and it just makes everything more complicated..which if she doesn't understand, she makes worse by continuing to act out. She's not evil, not right right now anyway...she's just..well, Jessi.

I think Jesse doesn't want to see Kyle be happy with Amanda. She doesn't have that kind of joy so he shouldn't either. Kyle has a great family, who all care about his life. Jesse just has a Dad, but she isn't even sure he is her Dad. Jesse doesn't know how to make friends. We know this because she thought that bringing attention to herself would make the popular students like her. This really didn't happen. I think she needs time to learn how to be around people to make some real friends. Its going to be hard, as she hasn't had the loving people around her.