First off, I'd like to say I'm sorry for what you're going through, I know it can't be easy for you. I've gone through a similar thing with roles reversed. I lived with the girl I was seeing for six months before she inevitable found out about my Poppy-tea use and she was absolutely devastated. Locked herself in the washroom crying for hours before she would even talk to me. She was kind of like you, she did some drugs in her teens but never any opiates, she really had no idea what I was going through. She helped me through a detox where I lasted a week and relapsed, and eventually, on my third relapse, that was it. She left for her parents on Friday and told me she wanted me out when she got back on Monday. Now, this is a bit different as you two are married and have a child together, and you say he's the love of your life. If you really care about him that much then you need to see this through, until you've exhausted every option. Make no mistake about it, opiate addiction IS an illness and he's NOT himself right now.
He's not a coward either. He may be selfish, but it's a selfishness that's brought about by the addiction, the illness. You say you've never done drugs, then you don't know what opiate withdraw is like. It's fucking scary, for sure. I don't know any addict who doesn't fear it more than anything. If he's in deep enough he may even fear it more than losing you and his child. This coupled with the though of living day by day without your opiates to fall back on is a scary thought indeed. You need to sit down and talk with him. Tell him that you understand this, you understand why he's afraid but for the safety of you and your child he can't continue to use. Then set up your boundaries. Tell him it starts NOW, not tomorrow, not next week, right now. He probably has a stash somewhere and he's probably going to lie and say he doesn't, or not show you where it all is, so you have to keep an eye on him. I know how hard it must be to be constantly deceived and lied to but it's all part of the addiction and there will be more to come, at least until the physical withdraw is through. But even then, recovery is a lifetime endeavor.
That being said, honestly and unfortunately, you can't do a thing unless he is willing to. He needs to realize what he's doing is damaging to himself and his family and until he realizes the cons far outweigh the pros, all you can do is help nudge him in the right direction. You need to be compassionate and supportive, I know this is hard given the circumstances but the last thing he needs right now is a shouting match. It won't do any good for anyone. Neither will kicking him to curb. Now this is also dependent on whether or not you love him enough to help him through this struggle. Kicking him out may solve your immediate problems but I can guarantee it's not going to help him out one bit. When my girlfriend kicked me out, my use damn near tripled. It's only going to make the self-loathing he already undoubtedly feels, ten times worse. I'm not trying to guilt you in to staying with him, if you're not willing to work for it as well then this is already doomed, it needs to be a mutual thing. But if he really is the love of your life then it's worth a try, right?
The first thing you should do is educate yourself as best you can on opiate addiction. Read up as much as you can about the acute withdraw, as well as the Post Acute Withdraw Syndrome so you have some idea of what he's going through. Be there to support him as long as he needs and urge him to come forward with you if he relapses. And he WILL relapse. Prepare for that now. Don't take this as a failure though, it happens to nearly all opiate addicts, it's part of the process. I don't know a single person who has quit on their first try. Hell, I'm on somewhere around my 10th try but it gets easier. But like I said, urge him to come forward with you if it happens, so he doesn't go sneaking around your back again. Don't scorn him for it, or he won't want to come forward with you and the lies and deceit will start again. Try to initiate a policy of 100% honesty. This will only work if you treat him with respect. Tell him daily how good he's doing and how proud you are of him. And yes, you should be proud if he's making it. Quitting opiates is the hardest thing I've ever attempted in my life.
I know you feel like you don't deserve this, you didn't ask for this and everything else. I know it must be hard as fuck but if you really love the man, and want him to be the father figure for your child, it will be worth it in the end. Best of luck to you, and feel free to PM if you need to vent or have any questions.