The question is, 'Why does attraction always lands up causing us pain?'
Not all attraction causes us suffering, while some do, and here is why?
Attraction often called 'love' has commonly come to mean only physical and sexual attraction. This serves only the animal aspects of our biological nature.
However, unlike other animals who merely exist in two major dimensions of the physical and the emotional, we humans possess the ability to exist in intellectual and spiritual dimensions.
We come alone, pair with people for different purposes and then leave this world alone. Our relationships with others define how we live. Humans are social creatures, we need to interact with other people.
It is generally believed that, opposites attract and likes repel. This is only partially true, for only in the physical and material world do opposites attract. In matters emotional and spiritual it is likes that attract one another.
Physical attraction is the least enduring for the physical changes rapidly. It is followed by material attraction which tends to be stronger than physical attraction. These attractions generally tend to be short lived.
On the other hand emotional attraction based on similarities in mind and heart tend to be more enduring.
However, the most enduring is the attraction and the love between two souls.
That is the wonder of friendship and soulmates.
With some audacity I have used the teachings of Rumi to convey the following.
I love my friends neither for their wealth nor their position,
for wealth and power come and go.
I love my friends neither with my heart nor my mind.
Just in case, heart might stop, and mind may forget. I love them with my soul,
For the soul never stops nor does it forget.
Fortunate are those who have friends and soulmates.