It seems that there is quite concrete way to find out if a group has reach a stage when a polarization of the group will split the it to two parts. When I was aware of this mechanism I became more calm and the split was easier to accept.
Mathematical analysis of the break point for a group. Read it because it could do your day some easier too!
This article points out that the dynamics for groups and relationships seems to have different mechanisms. For groups the high number of shared connections is good but for relationship more separated friendship clusters are stabilizing the couple.