Happiness is in Non-attachement, yes. But the word attachment may not be precise enough. Ownership sounds better. Being attached can be harmless to happiness but ownership over (or being owned) is the root of many heartaches. The issue is that when many are attached, they assume ownership. They feel they have rights over the life (or at least some aspects of the life) of the other. The root of that ownership is really selfishness but it doesn’t look that way until the other tries to exercise freedom.
Great article by the way