I really think your getting a bit too concerned about this, i mean if it was something serious like cocaine then i would totally understand where your coming from, the reality is as others have said weed is far less dangerous than alcohol and most people have smoked it at some point.
Mary jane is not addictive, it is a very mild drug and you cannot overdose on it.
Answering your questions,
I started smoking weed when i was much younger and like most kids i was just interested in what getting high was like.
Nothing keeps me from quitting i could and have stopped smoking pot for months before,
its just a fun way to look at life in a different perspective and enjoy things like music on a deeper level.
I hope this has helped you understand more about this drug, i suggest that you try smoking it to understand more about it,
you wont get addicted and you probably wont be so worried about what your boyfriend is doing after you have seen how harmless it really is.