This Guy Keeps On Saying Stuff That Isn't True

I'm so confused, I don't know if he means this or not, but currently I am a Jr High student and this guy my friend met on like...the 7th day at school during gym class keeps saying stuff like "Oh I love you, I want to marry you," and crap like that.

And ever since she "left" him for a while he's been mourning for her or as I have heard from some of her friends that he has. And after she came back from Health back into P.E., the girl found out that he was "cheating" on her for A LOT of other girls but he still treats her like she's his best friend/girlfriend/wifey.

Does this guy think she's stupid enough to believe him or does he really mean what he says? I don't think boys ever think before they act.