I recently found out that my boyfriend of a year and a half has been lying to me. He is a recovering heroin/ painkiller addict. He has been lying to me about money, and admitted to me that he has slipped up a couple times and used pills. He says he hasn't touched heroin, is willing to drug test, but I just can't believe a word he says anymore. I just had a miscarriage 2 weeks ago and he is taking it very hard. I am very worried for him and I was wondering if there are any ways I will know if he is using ANYTHING again?

If he is lying about money then he is most likely doing something again. Depending how much money per week usually gives it away for me. Like if it is $20. A week that can be cigarettes, beer and weed. $60. Or more a week he is most probably into something more serious like pills or heroin.

Keep watching and if he is getting progressively worse then you know he does have a problem.
Make it clear to him that you can not handle living through it again and you want him to be honest and get back into rehab if he does.
He is going to deny it but at least you made it clear where you stand.

Also notice personality changes, mood swings, his hiding and denying things and things like that.

If he's using heroin, you can always check for track marks (depending on whether he injected or snorted). Also, heroin users often rub their noses a lot and look like they are going to doze off - particularly just after they have had a hit. Slow speech and slow reactions may also be signs of use.

You had a miscarriage 2 weeks ago and you are worried for him and he is taking it hard. Im sorry but shouldn't he be worried about you and helping you through this difficult time? Heroin users are users in every respect of the word until they get clean and honest in every respect of their lives. Until they do, you can pretty much guarantee that everything that comes out of their mouth is a lie to cover their tracks or a manipulation to get you to feel sorry for them or an argument so that they can up and leave and go use for a few hours/days/weeks and leave you feeling like it is your fault. Living with an active addict makes you doubt yourself and errodes yourself worth/belief.
My advice, Get help for YOURSELF at al-non or other support group that will help YOU. They will give you support and advice on how to deal with living with a selfish self centred addict if that's what you want for yourself. He has to help himself you can't change him or stop him using - but you can make yourself strong! Best of luck x