Boyfriend troubles

So I'm 13 and my boyfriend is 12, we have been dating for 3 weeks and he honestly does not out much effort into this relationship. I don't feel comfortable around him and I wouldn't go anywhere with him with ought my sister with me. I just don't trust him. I like this other boy that has liked me and still does. I'm going to ask him out in a rap since I know he likes that. I want to break up with my boyfriend in a few days so I can ask out the other boy. Please don't judge. I know I'm young and these are probably just silly crushes but I really want to break up with him in the nicest way possible. How can I break up with him without breaking his heart?