Quick Answer: That's a challenging question. Thanks for posting [insert brow furrow and hands rubbing together in anticipation].
Change is often compared to death. "Change or die" was one of the mottos floating around the hallways of my graduate school. It certainly applies to organizations as much as it does to organisms.
Essentially you are asking about the reasonability of trusting someone after that someone has indicated that sh/e wants to change but has an "opps, I did it again". Without more of the context of your question, it would be too difficult to weigh the factors of that person's intent when sh/e told you sh/e wanted to change. Whether or not you should believe that person is going to be based on a number of factors:
1) your own issues with trust
2) the person's recent "track history"
3) the level of violation involved with this person's "rock bottom" experience.
For example, if a chemically addicted individual tells me in session that she hasn't taken a drink or taken drugs for one year and I see that this is true, I will have a higher level of trust that this person wishes to change in the direction of staying clean and sober than if she had only been clean and sober for one week (track history). I also would assess my own history of trust -- in my case, I have had so many clients not tell the truth because it is so difficult to do so, I often assume that they hide the truth anyways (example of understanding my own issues with trust). If a person has a complex cycle of addiction, compulsion, or shame involved with the "rock bottom" experience, there is a high degree of violation involved that may play into whether or not the person can change without very intentional intervention in the change process.
If the change is more on the relational level or about elements of one's character or personality, change can be slow. It may make more sense to re-evaluate whatever timelines or expectations are involved. A messy person, for example, doesn't usually become a clean person overnight.
The person may be telling you not only what you want to hear, but also what sh/e wants or needs to hear about him or herself. We really do want to believe that we can do good, that we can be good, and that others will be pleased with us. This is a noble and beautiful thing, and the desire to change can be acknowledged. But I would encourage that person to take it one step further and identify the small and large steps that would bring that change to life. Wanting to change and actually changing are two different things.
Best of luck to you! Let me know if this post helped.
