I would highly recommend you watch this video by Brene Brown. She discusses the vulnerability of relationships. Part of our coping strategy as humans is to realize that we are always vulnerable and to use this vulnerability in ways to strengthen ourselves and others.
Well this is a bit overwhelming at first, it provides us a way of savoring good things when they are happening, and sharing our vulnerabilities with others. In other words, the investment has to be to both celebrate the quality of the relationship when it is good, and share the vulnerability with each other when you are scared.