When I was pregnant last time I found out DH was smoking weed. This may not be a big deal to some but I was devestated.
Theres half a dozen men in my family/friends circle who do this (and though I'm not tarring all weed smokers with the same brush) they are all dick heads. Selfish and childish - due to the smoking I believe - its never something that is just occasional.
And it was the same with DH last time, i felt like a total IDIOT because I was oblivious to it and everyone else knew he was smoking :(
When I found out I jkicked him out for about a week, I really struggled though as we already had 2 kids, i was PG with SPD and we share all household responsibilities equally so it was very difficult to have it all on my shoulders.
Anyways, because he has mental health issues i was totally pissed off he would take weed as it does NOTHING for your mental health in the long run except make you paranoid (first hand onbservation of several men)
We had a longgg talk last time and he came home and promised me, PROMISED me he wouldn't smoke again.
So lasyt night his mate (weed smoker) came round to watch a fight.
At about 11:30pm I remembered I hadn't given the dog its 2nd worming dose so i got up to do it, they were in the back garden smoking.I didn't see but i could tell by DHs voice and giddyness 
he came in and didnt know i was oint he other room and put his jacket in the dryer to get rid of the smell and said 'i have to do that cause of how she reacted last time' or something liek that
he Oopened the door and i said 'you've been smoking'
to cut a massivly long story short, mate went home, he confessed, i cried alot he said it was the very first tinme hes done it since last time 
then he admitted he had carried on for a while after he came home last time but then did stop for the last year or so,
but he had been stressed so asked his mate to bring some yesterday morning :(
am just so upset,
to anyone who thinks weed is not a big deal, i don't care, thats irrelevent here, because I DO. and he knows that and he knows the strain and behaviour problems it caused last time and he promised me he would not do it again
and he broke his promise
i dont want him to leave, i dont think i can go it alone
i just wish he hadnt done it :(