I suppose like any break up people just have to try to analyse it and see what the problems are in the relationship and what, if anything, can be salvaged. But I am confused as to why one partner would choose to leave considering they still have one functioning relationship?
Why did one of the dyads break up? Is it because the NRE ended and they realised they did not have much else left to sustain a relationship? Well that does not preclude friendship and I do not see the reason why the triad could not continue to be a very loving vee unless one partner feels so rejected (the one that left?) that they refuse to let the vee work, in which case I would consider that the person who left probably had more attachment to the partner they broke up with and they are rejecting the other party by leaving. Therefore I would assume that the third partner would also be dealing with a breakup and well as supporting their existing partner through theirs.