Need help with an addict

Hey guys just need a bit of advice, my partner of almost 11years who we have 3 kids with has been using meth for the last 3yrs he hid it well, I found out several times and every time he has told me it's the last, I only have given him chances coz I thought If I don't help him who will, his family are enablers, and also because I knew him at his best and I didn't want him to end up like some lost junkie! So anyway I kept him at his parents house because of the kids but he kept disappearing and now I've just recently found out he's been cheating on me with some ice junkie girl and my gosh, I know some of you may think that this was inevitable but it still broke my heart like nothing else! All of this, this whole situation with the drugs and cheating has absolutely shattered any dreams I had of us keeping our family together. So since discovering about his cheating he hasn't been able to leave me alone the calls n msgs and the swearing he will never do it again and that he's serious now about getting help and getting clean, I never ever though I would even consider taking him back, and so that's where I need some advice please