When I quit heroin I started smoking pot so that I could "stay away from heroin". All I ended up doing was smoking everyday because I didn't want to be sober but I didn't want to go back to shooting heroin. Sure it keep me off my DOC, but it continued the active addict lifestyle of always trying to be high and not be sober.
Someone who is trying to achieve full recovery and is serious about being sober wouldn't use any mind altering substances. Being sober isn't getting high and altering reality. So while pot might be "just pot" to many addicts who did the "harder" drugs, it still isn't recovery and the chase for a high just continues.
Stick to your boundry, you are seeing first hand what chaos ensues from being with an active addict. Unfortunately, chance are he won't leave the house. He wants to keep things how they are, and chance are he doesn't believe that you will leave. Addicts tend to think that we are all talk and count on us loving them too much to walk away. The best thing you can do for yourself is cut your losses and get out of there and start new. I know it is alot easier said than done, but it might be the only way to get out of this mess.