It is always easier to be centred, zen, grounded and present when you are alone, when there is no one else there to disturb your peace.
It is always easier to be authentic, to be truthful when you are alone, when you don't have to consider anybody else's feelings or opinions, and you can say or do whatever you want.
Sometimes things just seem to be much easier when you are alone than being in partnership with someone. But then, life is all about relationships, relationship with friends, family and loved ones. To form relationships with people are somehow an inevitable part of life, and to avoid relationships is almost like to avoid life (of course, unless your path is to be out of the world).
I know many people who have walked the spiritual path for a long time, who have practised meditation and all different healing modalities for a long time, and even for people who teach about conscious relating and relationship, but when it comes to their own relationships, particularly intimate relationship, it may still not be so easy (myself included) - and interestingly, all my spiritual breakthroughs came when I was in some kind of relationships.
This is because a relationship is a mirror. In fact, any relationship is a mirror and life is all about relationships. In an intimate relationship, the mirror just seems to amplify ten times whatever is there in you that you are not so aware of when you are alone.
A relationship is a catalyst for spiritual growth. This is because when you are in a relationship with someone, the other person acts a mirror to whatever you are saying or behaving. It is a quicker way to reveal your shadow side, the unconscious that is buried deep down in our mind, that you may not be so aware of when you are alone because there is no one there or any mirror to reflect that back to you (and same for the other partner). You learn so much more about yourself when you are in a relationship.
If one can stay dynamically centred, grounded, zen, present and also truthful and authentic in any relationship, and if you understand the illusions of it all, to be in the emptiness of all things, to be in the world but not of the world. Whatever that happens on the outside will not disturb your inner state, then it means you are truly evolved.
But again, this is a moment to moment practice.
Even Enlightenment is still a moment to moment practice (because to me, enlightenment means to be in the present all the time, which means moment to moment). Enlightenment can be obtained if one is really earnest and can always dwell in the present no matter what arises.