Dating the wrong man
Triangles are stable when all three legs are connected.
What that means in a three-way relationship is that each day is securely connected.
As those problem must eventually re-emerge, the subsequent breakups are likely to happen more quickly.
Over time, and especially if they’ve been in disappointing other relationships, they miss each other again and valiantly try to “make it work.” If they don’t see those patterns and correct them, that process will occur until they either wear each other out or find someone they’d rather invest in.
Committed partners who still care deeply for one another, on the other hand, often separate because of external stress, worn-out interactions, infidelities, or a slow drift-apart that neither realized could have ended up in a separation.
They are at a loss when it happens, but still feel attached to their history, friends, children, financial situation, mutual families, and a deeper caring.
After a time apart, they realize that they want to make the relationship work and are highly motivated to make that happen.
In either case, a relationship they begin while being separated is just another kind of infidelity.