Is it because you think your time is more important than the person's who is waiting for you? Or do you just not care that you're going to be late?
I've had this for 15 years with someone and I'm sick of the excuses, like "we had to do X on the way".
The worst time was when they cancelled the night before because they had arranged something else 
It would be very difficult for me to not see them anymore, but I would just like to know how people get through life always being late and disorganised. Is it because you're always forgiven?