I don't think you are a hypocrite at all. Smoking pot is illegal, driving while high is unsafe and talking about it over your work email is unbelievably stupid! You have got to think about your kids- obviously your husband is not. I do not want to scare you even more, but if DCFS gets involved this could turn into an even worse nightmare for you.
Whatever your personal preferences about pot are, the health and safety concerns are very real, especially when you are pregnant and have a toddler. The fact that he is risking his job, driving with your daughter in the car, etc. shows that he is only thinking about himself- and not even that very clearly!!
First- is there someone YOU can talk to? A minister or social worker? Your local community center or village hall most likely has someone on staff that can give you some information and groups like AlAnon can be really helpful, just because they are familar with someone who is addicted to a substance and it can be really comforting just to know that YOU are not crazy and other people have dealt with the same things. Clergy of any faith often can help either with counseling or connect you with the right programs or people to help support YOU- as well as get help for your husband if he wants it.
Remember- this is not your fault. Your husband is responsible for his actions and their consequences, even if he doesn't want to admit it. (and I am sadly betting he won't) You need help and support too and do NOT be afraid or embarrassed to ask for it. Social workers and counselors have seen things and heard every story in the book- let their experience help you deal with this issue.
I am sure your husband will use the excuse that he 'had' to lie and hide this from you so you wouldn't nag him or be upset, etc. but I say that is bull. The lying is almost a bigger issue than what he lied about. The fact that he is emailing other women and asking them to smoke up with him or do lines is just one more betrayal.
I think you have to seriously look at the kind of partner your husband is and the kind of life you want for you and your children. Confront him and tell him you want him to quit the smoking and lying and that he must go to counseling- for the lying, as well as the pot smoking. If it were me, I would make it clear that you will leave him if this behavior doesn't change.
I would also get your parents or his involved in this if you have a good relationship with his family members. Drug and alcohol issues are hard for people to face and it may be that their support will be the thing that makes the difference both to you and to him. If nothing else, it will make it clear that you have a very good reason for acting as you do. Don't allow him to play the victim with his family and friends- he caused this situation, not you.
This is not just about you not personally liking to smoke weed or being 'against' it or something- this is about him lying to you and obviously feeling that lighting up with some other women is more important than being with his family. The fact that you are out of work and he is spending money on pot just makes it more of a slap in the face, IMO.
If you have friends or relatives you can go stay with for a little while, I would do that. Take yourself out of his life for a few weeks. It will give you a little time to think about things without him and sort out how you really feel- and it will give him time to see that you are serious and what life would REALLY be like without you there. Maybe that will be enough of a scare to make him change his ways.
Most pot smokers I know are not bad people. They are a little TOO laid-back for my taste and almost always seem to be late for everything. But they are not also liars- you can't blame that part on the dope. Just the fact that he has covered up the smoking AND meeting up with other women is a deal-breaker in my book.
I hope he can and will change. Best of luck to you- think about your daughter and your baby to be and be strong and do what is best for them.