When an adult twin finds a partner and the other twin is still single how easy is it for the single twin to remain pleased and excited for the other couple?
The sense of being left adrift and alone can be acute and the single twin can find themselves inadvertently or on purpose making asides about the suitability of the outsider. This in turn can place doubt in the coupled twin and cause a break in the new relationship.
Does this damage the on going twin couple long term? It seems it is hard but not impossible for either twin to individuate in the way sexual couples need to in order to fertilise the couple and keep the story alive and growing.
The third party needs to be someone, as discussed in the last twin blog, who is comfortable with their sense of self and knows that there will be times when the twins are closer than their twin partner is to them. Perhaps this is one of the reasons where successful twin coupling outside the twin relationship is with another twin who understands the dynamics.
There are examples of older twins in their last life stage having lost their sexual partner through death, divorce or separation turning back to each other for company and companionship. This becomes a safety net until such time as one or the other meets a new partner. The earlier pattern reappears and needs understanding and tolerance from each person in the triangle.