Wow, that is really sad that the bf is in such denial, but I certainly can relate to it.
For years I kept everything from Mr. Dev because I thought for sure it would put a strain on our relationship. Looking back, I wish I had been more up front with him because I think it gives the person (child) more control over the enabler.
I think you're doing the right thing by staying away and sending the message that you will not be a part of active use.
Got to feel sorry for him because it isn't easy being a codie either!
In time hopefully he'll understand that he isn't doing her one favor by giving her a soft place to land. By doing this the only get worse, but you couldn't convince me of that for years either!
Hope he sees the light sooner rather than later. In the meantime, you're smart to concentrate on you.
Hugs, Devastated