The Niddah period was given to us by Hashem as a big gift to help us GROW UP. It’s a gift, a way to strengthen the married couple to build a non-sexual bond in addition to a sexual one.
By forcing us to be married WITHOUT sex, we learn that marriage is about giving, sharing and emotional connection, not about sex.
Intimacy is just the icing on the cake that enhances the marriage and the Niddah period is what bring this to the forefront of our awareness.
We need to appreciate the time we are separate and work on learning what marriage is really about.
Without this break forced upon us by Hashem, how many of us would never grow up?