The reasons for relapse vary from one individual to another. Here are some reasons I have heard working in this field.
- Fear of success
- Fear of the unknown because things have been so bad for so long
- Guilt
- "I don't know any better."
- Loves the choaos
- "I don't give a "f*ck."
- Has a spouse/relative who won't stay clean
- Stress
- Brain chemistry
- "I couldn't stop the obsessions of craving." "The only thing I had was to use."
These are just a few I can think of off the top of my head. There are a ton of reasons as to why one relapses. It's up to the addict to verbalize and come to term as to why they do. My exabf actually had 2 reasons (fear of success and guilt).