I think that if you want to acquire a good gf you must be in a position where you are not dependent on a single girl turning into your gf.
If you only have contact to only one girl every single interaction you have with her will put so much pressure on you to not fuck it up that you can't act charming and light hearted anymore. Also it will force you to having to force yourself to accept every flaw in her because you don't have any alternatives.
If you put yourself into a situation where you can just move on to another girl on the other side you can always tell yourself that if this does not work out you can just move on to the next girl. This is the same psychology as in job interviews. When you can tell yourself that if this interview does not work out you can just move on to the next you will always perform best in job interviews.