Smoking cannabis doesn't make you any more, or any less of a person. It is simply a choice one must make in their lifetime, and if it is something you enjoy, why not? You should tell your girlfriend because it's not nice to keep petty secrets from each other. Just make sure you tell her you care about her more than you do cannabis!

It is harmful to the body,
it destroys brain cells and
really can effect a person,
but,
if you get addicted to it,
it CAN ruin your life,
and if you think your girlfriend would be ohkay with it,
you probably are wrong.
Girls are all about commitment,
she wants a man who not only wants to date but wants to maybe one day get married and have children,
and,
if her husband is addicted to drugs,
that is not the atmosphere she wants her kids in,
And I also think that will make her feel like,
(not trying to be mean here, this is just how I would feel)
I think she will feel likoe trash,
my sisters husband just got arrested for physically and emotionally abusing her and doing pot and weed.
It scarred her for life, know that he was doing those things (not just the abuse, the drugs to.)
So,
I really don't think she would be ohkay with it.