Also, one thing that may or may not apply here. If the boundary settings and boundary violations are something which your kid is even remotely aware of (or being made aware of by others), then what are you teaching him? Just a little food for thought, and something that might give you that extra push over the hill of resistance to maintaining your boundary.
You're a good person, Corri. Smart, too. If you've made this boundary, it's right. Forgive yourself for crossing it in the past, but decide it needs to be honored from here on out.
Hairdog, King Of Boundaries (as long as that's okay with you, dear.... )