How do I convince my gf's mum that I'm not in the relationship with her daughter for sexual reasons?

Convince her you are gay, and that going out with her daughter is just a way to get closer to a hot guy she knows.

You are not in a relationship with the mom. So don't waste your time trying to convince her of anything. Love your girlfriend, treat her well and the good relationship you have will be evidence enough for her mom. It may take some time. Although a year is quite a while at your age! Congratulations!

you don't. it will just take time for her to accept you. Moms are like that.

You can't, so why bother? She knows that real soon, she will be sucking your pole and you will be trying to put said pole in her hole, hoping to plant your cement in the hole....Mums know these things, just like her da knows!!!!

Why would you need or want to? Considering your age and hormone levels it will come up eventually. Be nice to her and considerate, be helpful and respectful and that should do it.

You can't. Be thankful that its not her dad that you have to convince.

that's the way they all start (sex eventually creeps in) LOL

you probably can't convince her ... you pose a threat to her daughter because to the mom's way of thinking, her 15 yr old daughter is still her "little girl" ... she doesn't want to think of her daughter having sex ... and actually, you shouldn't be having sex yet because more than likely (depending where you live) it's illegal, and technically statutory rape

show her and prove it to her that you love her daughter and are not in it for sexual reasons.. you can show her by not touching her daughter in anyway but to hold her hand and be caring around her, do nice things for the family.. kinda stuff.
good luck!:)

You can't, that is what mothers do. Have her put her kid on birth control if she is that worried about it. Problem solved

You're saying she's a platonic girlfriend?

Maybe her mother has a better understanding of human nature than you do.

Is your love sublime? without blemish and without self-interests?
Sex is one of self-interests, yah know.
Examine your motives and if desires swell within you, you are not what you think you are that your love is pure and undaunted without sexual strings attached and you would be a hypocrite to show her mom that you aren't when in fact you are.

Kidding only. hehe

Seems like a year is enough time to convince mom that you like her daughter. It may be the way you treat your girl friend or the way you act.