Disappointed with the husband

So i was going through my husbands backpack that he takes to work everyday to make sure he didnt leave any food in there since he didnt put it away like everyday. And i found a zip lock bag full of weed. We have been trying for our second baby for more than a yr and everytine tge subject of drugs would come up he would always reasure me that he was clean that he hasnt done drugs for about 3 yrs. And when i found the bag my heart sank and i got extremely furious at him for lying and not owing up to it. I thought we were over this part in our relationship since i stood by him for about 5 yrs while he tried to stop using drugs.