The new girlfriend is of course far better than the egf. that one has left behind. If this isn't a case one needs to learn to buy low, sell high.
Some people may well have frequent new girlfriends and others only a couple. It says more about them than the girls they date (as Americans put it, or 'go out with' as Brits say).
One thing that one should note with new girlfriends is that they will either never have been out with anyone else, or have a 100% failure rate in their previous relationships. Do not let this disturb you as it should be the same with you, and if it isn't true for both of you then one of you is two timing the other.
Everything will progress well until the new girlfriend becomes the girlfriend, upon her eternal journey towards ex-girlfriend status. If it doesn't then this a good thing and you should be happy for a long time. (unless she takes the ex-wife route, which is not where you want to be).