Oh Daisy, I am so sorry to hear that. It is great that he came clean with you, though... and that he is getting back on the horse. I feel like it's a good sign that he told you - he knows he messed up and came clean about it. That doesn't make it OK, but from my perspective, I'd rather have him come clean than lie by omission.
I can relate a lot to what you said. When mine first relapsed, we had the most wonderful 3 days.... He was so kind and romantic and wonderful, made the dinner, the flowers, etc. I was absolutely crushed when I found drugs in his car - I felt like the whole thing was one big LIE. I took it very personally, and it didn't help - he didn't use AT me. He is an addict. Addicts use. even if they have been trying to recover, it can still happen. Now it is just a matter of whether or not I am willing to have it in my life.
He also said he was afraid to tell me... didn't want to disappoint me, all that stuff. Again, I figured, that has absolutely nothing to do with me. I think when they know they have a problem and are trying to stay sober, a relapse carries a huge amount of shame and guilt. They don't want to have to admit it. That is the nature of their disease.... to hide the truth, to get away with things. They are sick. Perhaps especially when a girlfriend is involved, they do not want to admit a "failure" on their part; they don't want to lose her. That isn't because of something you or I have done to make them think they would. I think it stems from an inner sense of inadequacy, part of the "brokenness" that they try to fill with using.
You sound like you are doing ok... keep taking care of you!! This is going to be a long journey and it could become very painful if you can not detach. I will pray for both of you
best wishes