Help with a teen guy?

i'm 14. i'll just say that to start this off. ok i reaaally like this one guy in my french cl at school and we talk sometimes. i think he might be around 17 and my mom doesn't want me to date guys that old but i can't help liking him. he has a pretty steady gf but i was wondering how i could maybe get his phone number with out making his gf pissed off and without him thinking i'm weird. and suggestions or advice? please help!!! ~Jess