He did a bet with Draco Malfoy, if he could win you over, Draco would give him 300 galleons

Mattheo actually falled in love with you and when you are in the hallways, Draco appears

Draco: good job, dude. You winner her over. He says smirking and he gives the money to Mattheo

You: was I a bet?!!

Mattheo: no!! I didn't do any bet!

Draco: oh really, Mattheo? He makes you listen to a registrate conversation of Draco and Mattheo about the bet...

He did it...