Please help. I am having issues with this guy?

Ok. So I like this guy who is 13 and I am 12, and for the past month or so, signs have pointed to him liking me back. He gave me a small gift, he IMs me, etc. However, earlier today, he was flirting wtih another girl, who, although claims to like someone else, was flirting back. How can I tell if he likes me or her? And what should I do? Help is greatly appreciated. Thanks.