I also have no problem with pot and don't feel it should be illegal, and I almost never use *shoulds*.
And. Your post is so full of waffling, smoke and mirrors that I had to laugh out loud several times. You make promises, you break them, you rationalize, you lie, you absolve yourself, you tiptoe around the truth, you feel sorry for yourself, you feel regret, .... on and on and on it goes. If that's how you are with her, no wonder your wife doesn't trust you!
It boils down to this, as Aspiring said: you are constantly making choices that put your wife and child way, way down on the list of priorities, and you lie like a rug. To others and to yourself.
I know you are not going to suddenly start being straight just because I say it's a good idea. But I recommend that you take a very hard look at how much your behavior is costing you and your family, and see what inspired action you can take to scrape up some modicum of integrity in your life. If you don't do that, then your wife and child are far better off without you in their lives, and I think you know that and love them enough to want the best for them. If you don't want to change yourself, let them go with love.