I have had that issue too. When I broke up with Raga, I realised pretty much everyone I was in contact with was also his friend. A bunch of them were his friends and family that I had grown to like, and a bunch were my friends first and then became his as well.
Although he tried hard to become friends with all of my friends, I was "saved" by the fact that he doesn't speak French very well, so my French friends stayed primarily my friends, even though they have met and such.
But at the breakup, it was pretty hard. I wanted him to be able to get support, so I didn't talk to any of these people for about two months (letting them come to me if they wanted to) and by the time I tried to get in contact again, they pretty much reacted in a "stay away from me, you horrible person!" manner. And that could be because he vented to them during these two months, for instance, and they only heard his side of things (There is a French proverb that goes "he who is absent is always in the wrong."). But ultimately, I guess when there is a breakup most friends "pick sides".
I'm still in contact with exactly one friend we have (or had, I guess) in common, and it was really hard to lose so many friends, especially when some of them only met him through me.