I would feel confused also based on what you described. My thoughts are that he has been introduced to many new things, and has been asked to examine his life and where he wants it to go. Once upon a time I became addicted to prescribed meds which were opiates. I never went to rehab but did work with my doctor and a therapist. I felt somewhat vulnerable at the time and because I was home I leaned heavily on my husband. But had I been in a different environment I might have clung to that. I feel like this is probably only about him and where his mind is at, uncertain of what he's capable of and being in a new environment he may be shutting out the old and clinging to whats new. Extended use of drugs do alter the brain, but for most people it will return to normal. You might want to read about dopamine changes. A good site for info is National Institute Drug Abuse.
Id try to keep moving forward and take good care of yourself during this stressful time. Focus on what makes you happy.
He may be back around, he may not. Relapse is also common. Hopefully he's been put on medication to help. But his life probably wont be stable for a while. Your however need not be filled with anything but belief the life you want, and hopefully the man you are destined to be with will find you. It could still be him, but keep your options and heart open. Keep growing while your ex is hopefully doing the same.