Relationship blossoms beautifully while one is still unsure of its partner behavior... A poltically incorrect statement, but sarcastically correct one.
Generally in a new relationship, you steps forward your best foot, giving minute attendance to every wish of our loved one, whether explicitly expressed or not. We give them so much attention that our partner gets used to it. However, once relationship gets secured, we tend to get relaxed and withdraw the royal treatment which we used to give earlier.
Mostly, when the relationship is unsure, one tries to discover the other's life and also tries to become part of the other person's life. It is the time when both are totally focussed on each other's world and also they live in their own built world. But then, something shifts. Once the relationship is secured, the excitement of discovering each other's life and the uncertainty of the chase is over. Resulting into no incentive for putting the best foot forward.
One no longer feels the need to get to know each other's nuances and care for sensitivities; the price has been grabbed and the wall comes down.
One of the primary negative fall out of the change in relationship is taking the loved ones for granted and often forgetting them to give due attention. No wonder the loved one gets irritated with the neglected behaviour.
Based on the neglected feeling, they build their own space where they don't allow the other person to enter and upon entering, they closed the door on the other person's face stating you have ventured into a space where you have no business to be in. Both the persons realizes uncomfortable territory they are in, day in and day out. Even actual care and love at later stage will be misconstrued as intrusion.
One has to be very careful, how to put forward their word and convey their feelings. Even those closest to us need certain degree of formality and courtesy along with our required demand, by which they don't feel offended or feels that they are taken for granted.
For example, you may not think twice about carelessly commanding, rather than requesting, your spouse to fetch you a glass of water or make you some tea, but your spouse would, possibly. He or She would not react in the same fashion every time. One need to understand the other person's irritation and quickly address it. Else, the irritation builds up and soon may become bigger than the actual issue.
Hence, before acting or speaking to the loved one / closest person, steps yourself in their shoes. Just feel, how you will get irritated, if your loved one ignores you or take you for granted, intentionally or unintentionally. It is far easier to change yourself than to expect another to change. It helps to lessen own sense of irritability. And if we love them enough, accepting someone with all their faults and irritants will be lot easier and further it is an important part of loving.