I hate jumping to conclusions because obviously I do not know this guy from a hole in the wall...all I can tell you is my own experiences and past behaviors. I could be 100% off base ....with that being said....
My drug of choice was heroin and not crack..but a lot of the people I dealt with would also always be smoking crack so I was around it a ton and pretty familiar with it. Let me just start out by saying, a fan in a small bathroom would not cover up the smell produced from smoking crack. That stuff REEKS like burnt rubber and a mere few minutes of a fan on is not going to suck up the entire smell of it. Especially if you are going into the bathroom right after he gets out.
Another thing...being that I was a heroin addict ( IV ) I always carried my 'tool kit' with me wherever I was. This included, a small pack of q-tips, a soda can , and a bottle of water. I don't want you to jump to conclusions but as we all know, addiction is a progressive disease. I know many crackheads who switched from smoking to shooting because it was just a lot better of a feeling and addicts are always looking for a better, more intense rush.
Again, this is only my experiences while I was out using...might want to take a glance at his arms // hands for small red circles (probably the size of the tip of a ballpoint pen). Hope that I am wrong, but it never hurts to be informed. I hope you and your boyfriend make it through these tough times, there are better days ahead.