Why is it so hard to find a commited partner?

Up until now I had 4 serious relationships. The first 3 ended and the 4th is crumbling right now. There is something I noticed that they all lacked...commitment from the other side. From my side it's not a question...my BPD makes me commited even if I don't want to be. I'm always second, third or fourth etc. on there priority list...Am I asking for something impossible?