well jewelz when i was first getting clean, i had my kids help me to handle my own money, it was for my protection, money was a trigger for me. maybe thats whats going on with your bf, but the thing about that is, be prepared to just give it up if it ever comes a time that he decides that he don't want to do that anymore. what would concern me is that you seem to think that he's using this 20 dollars to use once a wk. addiction is progressive and a feining addict can get a tad bit dangerous.
maybe he has good intention so if it is working for you now, i would suggest for you to put away what little you can just in case he changes his mind.
my ah started out asking me to hold his money, but he got this bright idea that he could handle his own money after awhile and this is when he went back to using. i think that you are not nessassarily being codependant in doing that, maybe he really do need help holding on to his money and that shows responsibility to me, at least he's aware that if he keeps it today, he maynot be able to keep it for long.