So sorry you are going through this.
What you've described sounds devastating and very unhealthy for you and your daughter. Your story reminds me of episodes of 'Who on Earth did I Marry' to be honest. It starts out unbelievably great and spins out of control to very bad in a short period of time, with a lot of deceit in the works.
I also think your mistrust of him is well justified and I find it very worrying that he 'gets so mad' at you for being suspicious when he has proven time and again to be very deceitful and keeps on 'slipping'. Again, just the thought of those syringes lying around the house (although he may be attempting to hide them) is plain scary. You have your daughter in the same house (I assume he lives with you).
If you are unsure about whether you should leave him, I'd advise you to give that option some serious thought. You don't owe this man (not that you have mentioned yet) anything. He definitely should not fit your description of being the love of your life anymore since I don't imagine that you'd want the love of your life to be an active addict.
Please do seek out therapy for yourself and support from Al Anon and the equivalent for Narcotics. You have a long history with substance abuse (even though you were never the abuser yourself). You may have a lot of work to do to heal yourself.
Please continue to use SR. There's a lot of support here. I wish you strength on your journey.