Marijuana can caused drug induced psychosis and can cause the onset of other mental illnesses. Many people may use it without incident but that doesn't make it benign.
This... I know someone with marihuana induced psychosis, that over many years of use, he is now treated as a schitzophrenic (sp?), has anti psychotic drugs to keep him functioning. It is not a safe drug.
For the first thing, I hope I don't get in trouble for saying this but I understand that you obviously hate marijuana and drugs, but Marijuana itself is relatively benign. Absolutely this guy has wrong you in many ways.
But in regards to Marijuana, well up until several months ago I used to have it. Not all the time but a couple of times per week, and when I was younger had it all the time!
I would never act anything like the way you have described this guy acting. It is his personality coming out, and he has been deceiving you, and he probably can't deal with life and smokes pot to oblivion to try and escape, but Marijuana does NOT make people like that.
I know a lot of people that have it, and sure some people with addictive personalities go overboard with it and it become a mild to moderate addiction thing, but I know a whole heap of highly respectable people that have it. They don't tell anybody at all, and you wouldn't know.
A very close family member, university educated, great career, married, one kid and another on way, very patient and supportive of wife (NEVER aggressive), and he does it.
My 17, and 19 year old nieces, and this is not my choice, but they do it. They are lovely though, highly affectionate, bright and bubbly. They work and study. Stable, healthy relationships.
An old friend of mine used to date a podiatrist that was a regular user.
I could give you countless more but wont. I am not advocating it, but I don't think it should be seen the same way hard, chemical drugs are, which are much worst and more dangerous.
Threatening you with harm is absolutely no acceptable. Given how dodgy this guy sounds, he could possibly be doing other drugs but you don't know. Who knows he might be doing METH, now that is an AWFUL drug, I can assure you.
As much as I feel Marijuana should be legal, you may be able to use it to your advantage if you truly feel (and it sounds like it) that he is not suitable to be around your children.
Legally he won't get in much trouble unless he has a MASSIVE amount, but the judges in custody disputes tend to be more conservative, and it would likely add to your case. In regards to that, do what is best for your kids.
Marijuana is not benign, it does make people aggressive and can cause psychosis.