Before answering your question, may I just ask YOU a question, Robin? Please could you tell me why you chose to write 'I wanna' instead of 'I want to'? Did your teacher tell you that this was normal English? Is this what is taught in China? Did you learn somewhere that this is how native English speakers write? Or did you copy it from other learners? 'I wanna know' is not proper English. The only place that 'I wanna know' should be written is in the lyrics of a pop song, or the dialogue of a angry or impatient character in a movie or cartoon strip. You may not realise this, but when a native speaker sees 'I wanna' written down, we get the impression that this person is lazy and rude, like a spoilt child. If you want people to take you seriously, and especially if you want to people to help you, you have to write normal English. Now to your question.... 'Belong to' indicates possession, as in 'This house belongs to my uncle'. 'Belong with' has a different meaning. It means that two people or two things belong together. If you're helping me in the kitchen, and I say 'That sugar bowl belongs with the blue tea set', I'm telling you that that the sugar bowl is part of the set of cups and saucers, and that its proper place is with the rest of the set. If someone says to their boyfriend or girlfriend 'I belong with you' it means that it is natural that they are a couple and that they should spend their lives together. It means that being with the other person is their natural place.

The book belongs to me. Matthew and I love each other, we belong together.