As far as I see it, once the two of you split, you were both free to be with whomever you wanted. My issue with your ex is that he lied to you. Is this one of the reasons you two broke up in the first place? And not for anything, it doesn't matter if you were with him for years and didn't use a condom - are you going to put your life in his hands? He's obviously now just put you at risk.
I think you need to examine why the two of you broke it off in the first place and why you really what to be back together with him.
Hey if it works out, then I'm very happy for you. But make sure it's for the right reasons and in your best interest.
Good luck.