Relationships start in many different ways. It could be a sudden burst of electricity or the slow burn of sustained familiarity. No matter how things start there is a whole industry built around telling us how to keep them going. When I was young the importance of respect was drilled into me as the key ingredient in all relationships. Respect for elders, those in authority, and the head of the household. The notion of romantic love was seen as something very insubstantial that was a byproduct of a decadent western civilisation.
It is the test of time that truly determines whether a relationship is for real. And in any relationship you need to have both love and respect present. However, over time both of these change in a relationship. Very often that overwhelmingly passionate love that was there to start with gradually settles into affectionate caring. The feelings may remain the same but their spontaneity and expression become somewhat dulled. Over time there are a lot of things that can erode respect in a relationship. It could be male insecurity, a reversal of fortunes, sexual dysfunction, irritating personal habits or infidelity. If these conditions persist it often opens the door to bickering and disagreements.
A good relationship needs love to thrive but without respect a relationship has minimal hope of surviving.