When I first found out my AH was abusing opiates, I did the same things you are doing. I went through his phone records daily, snooped through his things and went through his truck at least once a week with a fine tooth comb. The better the detective that I became, the better he became at hiding his pills. It was a vicious cycle until I finally said enough and stepped off the merry go round.
Leaving Rehab after 12 days is a huge red flag.. You shoulden't have to ask him to go to a meeting with you, if he wants to get clean he would have already been doing that, the minute he stepped out of rehab.
For my own sanity and well being, I had to step away from my addict and mind my own business. It was hard at first because I was and am very codependent. I thought that I could fix him, I thought that if I busted him enough times with drugs that he would stop, I thought that if I could go to meetings for him that I could help him get clean, the list goes on and on and on... I had to learn some very hard painful lessons in order to change my way of thinking. Detatchment is hard and sometimes it takes more then one try to get it right but really it's the only thing that you can do and it's the best thing that you can do to help your BF.
Find some Naranon or Alanon meetings for yourself and go to them.. If your BF is serious about recovery he will seek meetings out on his on.
Good luck to you