is she a good girl friend? boys and girls please come in.

as i said before i got a girlfriend, which is havin fun in aus. ( for more information check my last question: "what can i do?does she really love me?") thx. things was gettin fine, thn another problem head up. fkin hell ya? another boy came up to her ( friend of her) ask her to go out, jst two of them. i mean if ur girl friend tellin u a boy ask her to go out, wont u get pissed ,angry, jealous? wont u tell ur girl friend dont go out wif the guy? well i did.. and wt i got is. "hes jst a frd"
yes hes jst a frd but then hes kinda lik my old enemy whos tryin to steal my girlfriend before. if ur me would u like sit and do nothing? cuz theres a "might" after tht "date" he might stole my girlfriend, i mean who wil no wt they do... right? is not tht i dont trust her but still... plus they never see each other before... its their first meet.. two people? everytime i try to ask her plz dont go out wif tht guy.. she will be like " hes jst a frd", "we wont do anything bad", we never seen before"...
before she have promise me she wont go out wif guy lik one to one and not gonna see tht guy. cuz i no tht guy still wanna steal her from me. and now he can anything on tht date. and i cant do anythin.. i have already told her ask mor frds to go wif her. but im not sure will she listen..
for boys do if ur girlfriend is goin out wif a boy one to one, wt would u think? and to girls, if u have a bf already, will u go out wif boy one to one?
again this question is wt should i do? dump her? find sumone better? but she always say she still love me..