Mature love is expressed well with wise observations on life.
Love is not one smooth highway to paradise. That's the reason why so many fall out of it unable to meet the challenges posed by it. It is best expressed in the lines:
"And even though there's ups and downs
we must go on, even how unfair it seems..."
There is nothing "unfair" if love calls for certain conditions to be followed. But we are just human to feel the pain, sometimes unbearable.

Refreshing the mind with the happy days of past is a sensible way to keep the present pleasant.

A small suggestion with the following lines:

"And even though there's ups and downs
we must go on, even how unfair it seems..."

"even" is repeated through the second line which I think can be avoided thus.
"And even though there's ups and downs
we must go on, however unfair it seems..."

I hope you don't mind this intervention. You can ignore it if you so desire.

Write on!