I'm not going to jump to the conclusion he is an addict. I had my longish period of using for recreational purposes without it becoming all crazy needful addiction. Oh yeah I had that period of crazy needful addiction as well. Thus ended my sports career as a marathon speed user.... :biggrin:
However, I know of people, We will call them friends just for simplicity of labels here, however they have been using on a regular basis since we were in our twenties. So figure at least 2 possibly 3 decades of regular recreational drug use. The survivors (lots of the people I have known have died, which is odd I was voted as the one most likely to die before age 40), have their lives in order, have jobs, relationships, etc - most are doing better than myself in these areas - much better.
This is the terrible secret of the Modern Prohibition Era - people are all focused on the Faces of Meth websites and not looking at the far, far larger group of people who use regularly, hold down jobs, careers, hold families together, etc and never lose control.
This same approach is what lead to the Alcohol Prohibition. They focused on the down and out tried and true alcoholics and failed to mention the larger population of responsible drinkers.
So you need to first know if your BF has an addiction, of if he can use occasionally recreationally without it being a problem.
Assuming he can use for recreational purposes and likes to party just a little, you need to look at your relationship and assess if you have a prohibition leaning, meaning you just flat refused his use of drugs as an option. If so, and if he doesn't really have an addiction problem, you may need to seriously reconsider your stance on this prohibition and compromise.
The deal with his looking for drugs while out and about via the internet is that he is standing a much, much greater chance of being arrested. Assaulted, killed, whatever. Statistically he is safer walking on the wrong side of town in the middle of the night and asking a passing stranger if they are cool and know a connection.
He also will need a safe environment to use his drug of choice in. Just like its not recommended to drive while drinking, or swimming while pissed three sheets to the win, there are safe environments to use in and unsafe ones. Random motel rooms out on the road are not actually that safe, especially if you are making deals with strangers off the internet.
Now if he has an addiction problem - He NEEDS drugs, not just wants them (a big difference) then this needs to be handled in an approach which is safe for both of you.
Demands do not work. Forbidding does not work. Promises of dire consequences will do nothing but send him deeper into hiding his little problem. He needs supporting suggestions to guide him to seek help.
IF he is addicted to drugs
YOU need a support group yourself. That would be Alanon/Alateen:
http://www.al-anon.alateen.org/
Lets say you already know that drugs and him end up to serious bad shit happening. I strongly suggest you use Alanon/Alateen to find a local support group and get yourself to a meeting right now.
Do not stop and ask questions about what you saw on facebook, don't confront the partner. Get yourself a support group, and talk with them about the details of his little habits and how those have been problems in the past.
Right now there is way to little information for me to even start making suggestions as to how to really approach this issue with him without it leading to lies and hiding his habit and him going deeper into addiction.
Confrontation rarely works to actually fix addiction. There are other methods, methods that members of Alanon/Alateen have used with tried and true results - but those result are by each case and they are going to want to know much more about his drug history.
So to recap, if his use of drugs is not an addiction, then you need to open up to the idea that he uses at home, in a safe environment, that he finds a trustworthy dealer (at home), to reduce the risk of arrest or being killed out there in his job travels.
If he does have an addiction, you have sufficient evidence for you to seek out support for yourself FIRST and then with those people figure out an approach that is safe for both of you.