What is relationship without love? Sure, we can have all kinds of relationships to others, involving various negative dynamics: lust, pity, intimidation, excessive dependence, etc. But the only truly healthy relationship is a loving relationship.
Love is what makes relationships both valuable and viable. Love is what makes enduring relationship a joy, not just a test of endurance. Without love, relationship simply won't work -- at least not satisfactorily. Therefore, love is the essential requirement for good relationship.
Such is the connection between Love and Relationship.