fight or flight

Relationships.
One of my favorite things to talk about is relationships. One of my passions is relationships - every single kind. The thing I probably think about the most is relationships. My relationships with other people, whether they are plutonic or romantic, my relationship with Jesus, high school student's relationships with Jesus, my friends' relationships with each other, marriages, friendships, parents and children, you know, any kind of relationship that you can have. I think that's why Grey's Anatomy is my fave show because it is based on relationships - and all different kinds of them.
Here's my questions... When do you stay and fight for a relationship and when do you let some of them die? Is it ok to let some relationships fade out or should you try and fight for and ultimately save every relationship you've had in your life? Which ones are the most important? How do you determine this stuff? When you're just dating someone and not married, how do you know whether to fight for the relationship to work or end the relationship completely. Outside of a marriage relationship, there is no actual commitment. So how do we honor this unspoken commitment that happens between friends?