Well, I think the issue of the OP, interestingly, was that they were smoking in her garage. The effect on her b/f's lungs seemed to be a secondary issue. In my mind, the guest did everything possible to minimize his impact on them. There seems to be no pleasing some people. She's right in not inviting him back, if it's going to cause that much of a problem, but one has to wonder how long can you live in a bubble. Are they going to cut ties with every friend who isn't their ideal version of a person?
I think a little education on what cannabis is and how it's been used over the last 4,000 years is in order. I think many of us will see MJ decriminalized in our lifetime anyway, may as well get informed now.