when picking up girls, don't mention the fact you have a gf, it will make it sound like your braggin.
but if you somehow get onto relationships and they ask you or summin, just say 'im sorta seeing someone, but its not going great' so they still think... 'oooh he's open'. but make sure you say as though your embaressed to admit it, then neg them for not having one or if ther in a proper relationship 'well i bet its good to have someone that will do and drop anything he's doing just for you'...she will usually say 'well thats not how it is, its not prefect etc etc etc' she's basically tearing him down for you which means you don't run the risk of appearing like a jerk.
^that was a lil bit off topic
but no, having a girlfriend doesn't put you ahead of other PUA as it all depends on skills, even if you've got the same skill set as another PUA, your chances are equal.
-teen