This is hard, and there is no one answer, but a complex answer:
The hard bit first. Sometimes friends met through friends can leave the "original" friendship behind in terms of things in common. I have found this, and I do feel guilty about the "original" friend (A). A and I are still friends, but B and I just really hit it off.
But let's temper that bad news with: What they have in common could be as simple as being there and available to meet. This is quantity-time, although it does have the potential to turn into quality time if there's enough of it.
There are probably two ways to get out of this dynamic: tell your friends how you feel and ask for more time with them (they may feel flattered); make friends with people who understand this situation (e.g. people who have been expats). The latter point was really crystallised for me on a thread a few weeks ago, in which people were saying how sad they were that their families at home were forgetting them while they were abroad. We have some friends who are moving abroad shortly, and I realised how lucky they were to have both sets of parents living abroad and simply used to the kind of effort one has to make.
As for meetings, something we do sometimes is to visit a city where we know a lot of people, and choose a venue to sit in all day (a pub with a garden is a good one, in summer, or even a leisure centre, not as strange as it sounds, since leisure centres can have decent cafes), and hold court for "drop-ins".
Good luck in finding your way out of this. It's a bit depressing, so I do feel for you.
P.S. I'm sorry for the "stalker" question, but are you the "frakking" nanny? 