5 years, 3 kids, drug habit and lies......should i kick him out?

We have been together for 5 years, have 3 children, youngest is 6 months old. He had an intravenous drug habit when we met, but he managed to hide it from me for nearly a year before i caught him out (stupid me). The drug habit has been on and off for years, and as far as i know, he is no longer intravenously using drugs... as far as i know anyway... and he seems to think he needs to hide it from me when he is using. He lies, steals money from me, and generally puts the well being of our family in jeopardy, finacially. I think the lying hurts the most, i could cope with the drugs, if i knew what was going on. He isnt a full blown junky, he can and does quit for months to a year, but he always ends up back on it. I have given him so many chances, but last time i told him that 'that's it, no more', but i caught him out last night, he denied it, even though i was waving the proof in his face. Hes a good dad, loves his kids, and he does mean well, he just doesnt think. Cont...