I Want to trust my bf again!! Help!?

Well, we r both really young . I'm 13 and he's 12. I know its a young age so I don't wanna hear about it. But we have had this relationship going on for about 1 year and 6 months. And awhile back he did something very stupid that you wouldn't expect from someone that young, it was about 6 or 7 months ago. <--He did cheat on me once...and it was pretty bad. But most people told me to forgive him. So we still dated, and we still are. But I'm having bad trust issues lately and I'm not ready to leave him. He lies alittle and that doesnt really help any but I always just saw that as immaturity. Someone please give me some advice. ):