OK before I start please DO NOT be rude!!

Okay so my fiance and I have have been TTC for over a year now and we have had no such luck. I have been taking prenatals for like 4-5 months. But my fiance smokes weed every day. I do to but its like once in a blue moon. But I have been told that weed can kill sperm? I don't know but how can I get him to stop smoking just at least long enough to conceive? He wants a baby as bad as I do and were just about to give up BC I it's been close to 2 years that we have been trying. Please help?!?!?!?!