“That person is lonely who has no one for whom he or she is Number One.” – Helene Deutsch
Do not try to be The Only Thing to someone for it is not healthy, unsustainable, isolationist, and does not foster growth for each partner. Strive instead to be Most Important. Be the One that drives and empowers, the One that they love and desire and grow for, but there must be Others that diversify and balance and allow you to grow as a person so that there is even more of you for that Most Important person to benefit from.
Being Number One means they (or you) are not the entirety of the other person’s existence, because that would ultimately lead to stagnation, decline, and an inability to survive on your own. But Number One is an enhancer, making life better and richer by having the partner to share it with, a wingman or woman that can fly high and celebrate with you while having your back.
Being the Most Important (but not Only) Thing is the most important component to a great life.