I guarantee you'll look back two years from now and regret that you didn't do these things -- I guarantee that.
Acc
This is near-100% what people report from their situations. I could even dig up some old threads if you'd like where we all openly talked about it. Nearly everyone agreed that they wished they would have drawn much stronger boundaries, early.
Starsky
I totally agree with this, I just want to add that it is NEVER too late to start.
And people are going to do what they feel comfortable with, they don't change until the Pain of changing is less than the Pain of staying the same.