Age-13..Me and my Best friend. We'll call him.. Sam. Well, he has a girlfriend and me and him text like crazy. Every night when I go to bed though. He says I love you (friend) I say it back. I really like him. Also he sends me these love forwards he doesn't send to his girlfriend. I'm flirting.. But is he? When I'm sad he always says it drives him insane. And day he talks to me during locker breaks. All my friends think he likes me. But my best friend, we will call Carly, likes him.. She doesn't know I like him. Plus he doesn't like her... What do I do?

Advice
He seems to want to have two girls at the same time. This is nice for him but not nice for you and his girlfriend. Yes he does like you.
I think it's time for you to ask him if he is serious about his girl friend. If he is then back off from the flirting. It isn't fair to his girlfriend.
But, if he says he is ready to break up with her then go ahead but slowly. You don't want to be the cause of a break up.
If he breaks up with her then act fast! Find out from friends and family what fun activities are going on now. There are tons because it is the Holiday season. Everyone likes to have fun this time of the year.
Hope this works out for you! Happy Holidays!