Some people tend to get addicted to things more than others. There is a gene that is in charge of our tendency for addictions.
If you only smoke the weed once ot twice a week, in a party or with a friend, you're fine.
My boyfriend smokes every day, a few times day and it has ruined out relationship many times. I see him lose grasp over life, can't concentrate, dropping classes, being broke, spending money on weed when he has no money for food...
And the sex drive, lord, boys, I am a sexy girl, and he just wants to chill, or play a computer game, or just fall a sleep.
I am close again to that point of ending it, hoping I'll have the strength to make it final this time. After 2 years, I should have learnt I can't change him. He has to change for himself, and I can't wait forever.
So...don't let it ruin your life.