I have experienced that, but only during highschool. Most mature women (and I'm guessing men) don't disappear when they find a love interest...if anything, after the initial 'getting to know' the new bf/gf, they want very much to include them with their friends. Sometimes, it's to gain approval, sometimes to show off...sometimes, both. At any rate, if your friends are still stuck in that loop, then I suggest they are still on the same maturity level as teenagers....as you suggested.

Try not to take it personally. Fact is, if they can't come to grips with 'sharing the wealth' with their good friends...odds are they are also smothering the bf/gf...and the relationship is doomed anyway. Just wait a few months.

Take care.