Reed30,
I've been there too, it's hard. I was never around drugs either and my exAH hid it from me for years. When I found drugs in the garage and confronted him he laughed in my face, called me stupid because he had been doing drugs for years and I was too dumb to notice. He was finally fired for selling drugs from the Fortune 500 company vehicle.
My exAH's problem got progressively worse - he was forced into rehab to keep his job. When they have to go and it is not their decision the chances they will continue to use are high. Rehab is a lot of work and can take years before the addict is on the road to recovery. It is not uncommon for the ones with the best of intentions to replase a few times before they finally make it. Even then they are recovering addicts for the rest of their lives.
IMO you are very smart to break up with him. If he truly loves you, if he is truly serious about working his program, you'll know soon.
As you can tell from reading the posts on this forum (and others) addicts are usually expert liars, look how well he hid this from you for so long. Addiction is expensive, we lost our home, everything, and I was left to raise my children on a clerical salary with zero child support. And the possiblity of prison is very real for dealers, plus it is a dangerous activity and he is putting your life in danger as well.
Start a journal, be very honest, you can even cuss! You will slowly start to sort out your feelings. Trust your gut.
It's good that you are in therapy.