People change.
Not necessarily a bad change, but still,
Feelings, wants and needs,
Effect the algorithm, if you will.

Suttle changes to them,
May hit ****** hard to you,
Doesn't stop them caring,
But it can still feel painful, true.

You may crave for them to go back,
Back to the way it was before,
You can try and forget too,
You might even crave them more.

Sometimes personal situations,
And their own hardships are to blame,
Your might too,
But you want them back all the same.

Sometimes its hard to question,
And ask what has changed between us,
But you don't want to fracture what you have now,
Don't want to cause a fuss.

Chemistry.
The complex emotional or psychological interaction between individuals,
Some times the results a great,
Sometimes you mess up the concoction, unintentional.