Relapse is a reality for most addicts. What you have to do is identify where things went wrong and put a plan in place to fix it. You HAVE to make changes or the cycle will continue. For one, like you said yourself, you can NEVER as an addict let your guard down. You could be clean for 20 years and STILL relapse. There is no "cure", only management. That was one of the biggest things that led to your relapse. Had you had a plan in place, you would have identified that you were struggling with cravings and feeling lousy, and you would have employed different (healthy) coping mechanisms to deal with that...even if it meant you had to go to a meeting 3 times a day, or call your sponsor every hour.
You need to formulate a solid plan for aftercare moving forward. That will involve things like NA/AA meetings, addiction therapy, etc. You must learn about the stages of relapse (a person relapses LONG before they pick up a pill), and learn how to identify triggers and what to do when you're feeling vulnerable.
You must make sure you eliminate any and ALL sources, and confide in a few people you trust. Support is paramount to addiction recovery too. If you keep it a secret, it will be much easier for you to use behind that secret. Essentially you have to put up roadblocks for yourself, making relapse VERY difficult. You have to be accountable and take control, and KEEP the control. GETTING clean isn't half as hard as STAYING clean, yet most people only focus on the detox part, and that's where so many people go wrong.
Best of luck to you, please keep posting, you will receive loads of info and support here. When you post again, start your own new thread, as this one is old and will likely get passed by by many responders. To start a new thread, click here: