Let’s leave the biology behind and say that true love is the state you are in when you feel connected, attached, and happy with someone. It is a place where you feel a permanent sense of connection with someone else, regardless of what happens.
In addition, the definition of true love goes far beyond what your body does and feels, or how you view someone in a relationship. True love can also be defined as you how you act in a relationship with someone.
True love is about meeting each other’s expectations and loving each other with trust, acceptance, and support. True love is about treating someone with the kind of respect that they deserve because you view them in a loving manner. 
True love is about the way you perceive someone. If you can step outside of your ego and see the value in someone else and the value in forming relationships with some give-and-take, then you can develop the mental attitude towards someone that results in a loving bond that can’t be broken.