Husband lied about drug use. (Long)

A few days ago my 2 year old daughter picked up a straw in our bedroom, I only noticed because she said "tiny straw" as my husband immediately took it from her and shoved it in his pocket. Later while he was at work I took it out and it had white powder in it. When he got home I asked if he'd used cocaine and he said no. When I showed him the straw he got very quiet and then told me he used when we went out Saturday night. His explanation for lying was that he was scared and didn't want to upset me because it was a one time thing. I'm having a hard time believing him because he's been working later than normal, sneezing a lot and has a constant runny nose. I'm not really sure what to do or say to him because now I'm constantly thinking about it and wondering if he's still lying. Opinions?