Scout is falling in love with Dill, and she is confused about the mixed signals that she is receiving from him. Dill has already asked Scout to marry him, but
... then he promptly forgot about it. He staked me out, marked as his property, said I was the only girl he would ever love, then he neglected me.
Despite his intentions toward Scout, Dill seems to prefer spending most of his time with Jem, doing things that little boys do. Even when Scout "beat him up twice... it did no good." Jem and Dill only allows Scout to join them when they "needed a third party," and since she doesn't approve of "their more foolhardy schemes," Scout ends up spending much of her time with Miss Maudie. Since Scout and Jem have always been nearly inseparable, Scout is feeling left out since her brother has found a new playmate--a boy--more suitable for the "male superiority" that seems to be infecting him.
In chapter 5 of To Kill a Mockingbird, Scout is starting to mature. She is frustrated at Dill because he is sticking closer to Jem. Dill and Jem are spending more and more time together and Scout is a little jealous of this. She feels left out and overlooked by the two boys.
Dill was becoming something of a trial anyway, following Jem about. He had asked me earlier in the summer to marry him, then he promptly forgot about it. He staked me out, marked as his property, said I was the only girl he would ever love, then he neglected me. I beat him up twice but it did no good, he only grew closer to Jem.
Scout is jealous that the two boys are becoming closer while she is being left behind. We see that Scout is confused about the things she is feeling and what people are saying to her. Dill told her he loved her, but in the next instant he is ignoring her. All of this is strange for Scout, and she is discovering that the more she grows up the harder things are becoming for her to figure out.