Like someone else said I read your posts with sadness. What you are describing is classic addict behaviour. The addict in him will run roughshod over you as you are for the most part (no offence here) clueless re; drugs.
You want to believe him, that makes it harder for you and easier for him.
The only thing for certain is that if he has been using crack, he has a problem that is going to be hard to resolve.
You need full 100% honesty about it and full cooperation from him in rehabilitating which means his behaviour needs to be 100% transparent. Phone conversations, numbers, aquaintances, friends, whereabouts, money.
By having him in the house he gets the best of both worlds, by making him stay elsewhere he may see what he's losing.
He may very well just be pleased that he can get on with using without being hassled for a while. It is very early in the addiction for him. It may very well have quite a long time to go.
Depression goes hand in hand with addiction.
The other posters are right. Until he admits a problem and states a desire to fix it you can't do anything except hide your jewellry and anything worth hocking. Secure your bank account, tell the DCs Dad is sick but will get better eventually.
An addict usually needs to hit rock bottom before they will admit / commit to serious rehabilitation and even then relapses are v common. It may take years to 'resolve'.
I am so, so sorry for you to be facing this after 20 years and three kids together and I so hope this runs it's course sooner rather than later for you.
I'm sure you will find a multitude of support from MN who can direct you to other resources.
Good luck and best wishes.