There comes a point when the pain experienced by contact with the addict is so much greater than the pain or fear felt when in no contact. It's usually not strength per se as much as it becomes a matter of self preservation.
As time passes and serenity is felt in the absence of the addict, then it becomes easier...again not as much a matter of strength as it is a matter of feeling better when they aren't around and finding relief. Eventually that feeling of serenity or relief becomes the desired feeling. And no contact becomes even more easy to maintain.
There is always a period of significant discomfort (anguish) before getting to that point though.....looking back on it......that's the really tough time.
Take care of you.....first.
gentle hugs
ke