What does Backseat Best Friend mean?

Backseat Best Friend meaning in Urban Dictionary

When your some ones companion for a lot of time, after that once they drop each of their good/best friends they cling to you personally. Then around 6+ months later on when he or she gets people they know straight back, they start pressing you away slowly and moving towards their old buddies again, but still phone you their best buddy.Situation is created worse when stated individual can be your Ex and you have feelings for them.