Do old habits die?

Years ago I had a bad experience with a friend, when I first confronted the individual about my findings, there was no admission to any wrongdoing. I chose to believe the explanation given at that time but as some things became more apparent, I decided to look into it and uncovered more things to suggest that my original concerns were in fact valid.

After months of confronting the issues, the individual changed and stopped the tendencies that caused the conflict. Since the change the friendship flourished substantially and I was thrilled. Without the issues my trust began to grow and I was more at ease.

However; in the resent past I noticed that the individual was slowly reverting to the old habits that previously brought commotion and turmoil. I didn't want to bring unnecessary negativity so I watched from a distance and came to the conclusion that as per my suspicion some prior tendencies had resurfaced.

When it was convenient I inquired of my suspicion but the question was not well received. The individual wouldn't even answer instead I received absurd accusations which is unfortunate because this new development leaves me with resentment and no desire to pursue a positive resolution. I have even began to wonder if there are certain behaviors that don't really go away.