Love is something pure which doesn’t need a particular day to be decreed in order to be celebrated. In fact the love that you show to your spouse must not be confined to only one day of the year but it has to be shown on daily basis.
When you show that love to a person who is forbidden for u in a forbidden way then you end up in making this society more promiscuous. And Islam is a religion which eradicates all evil from its root and hence Allah not only orders us to stay away from evil but also to not follow even the footsteps of Satan!
May Allah help us to understand this religion which teaches moderation and balance in both, this world and our quest for the hereafter.